As some of you might have noticed, IC2's recipes have been different the past few days. The textures too, changed shall we say. Even the tiering of newly placed cables and EU storage blocks had changed compared to what you might have expected. Whilst a couple of people were concerned by this, I do assure you this is in fact intended, if by no means permanent. Let us explore why...
2nd April 2011 is the oldest public release of the original IndustrialCraft, it is still available to download on the wiki. There might be slightly older ones if you look hard enough, but practically speaking there is no benefit to having those, thus is besides the point. Given this, IndustrialCraft as a concept is 7 years old. Whilst the actual date is some time in February, this release is as good as any for a first marker in the journey of IndustrialCraft development (and a good excuse to do all this on April Fool's day :P).
Fast forward to the 29th August the same year, the first public (beta) release of IndustrialCraft² is put up here (it too still available if you want). This was the first key overhaul that saw cables go from being clunky whole blocks that ticked once a second because the energy flow code was so slow, to the smaller tiered cables you would recognise, as well as large content additions and changes to pre-existing content to improve the standard of the mod. Whilst still unrefined in this form, it was a big step into creating a full IndustrialCraft experience.
Having largely carried on along the same track (besides a reactor overhaul for the 1.3 update released mid-September 2012), the next sizeable change was the entering into IndustrialCraft² Experimental. This happened August 2013, and saw the partial reworking of large parts of the mod. Such changes included the many recipes, textures and tiering. Having existed for several years, these saw the removal of many iconic features IndustrialCraft previous had, such as Refined Iron and textures like these: 
Having done some of these changes, not everyone was happy with the resulting replacements. Plates for example, added purely to avoid recipe conflicts from IndustrialCraft's heavy iron usage, were disliked from the additional crafting complexity associated with them. Equally there were people who were unfazed by this. It was simple yet divisive changes like this that assisted in the decline in usage over time, not ignoring the other more noticeable ones like the energy net being largely disabled.
In the present day, looking back makes these events all seem deep in the past. For many, IndustrialCraft² Experimental is the only form of IndustrialCraft they remember, or even have ever played. FTB's Infinity Evolved a common exposure resulting in people using it that otherwise wouldn't have. Yet the legacy that the previous versions had left are fundamentally imprinted on those who remember it, be it through their experiences with Tekkit Classic, FTB Ultimate or other packs now many years old too. They were in many ways simpler times, for better or worse. This is the true IC2 Classic that people foretold about. Really it is these people for whom build 73 is aiming to find, those that will look upon the recipes and the textures to recognise them as what once was. For those that don't I apologise for the inconvenience/confusion, you can use build 68 or below to have all your new (or are they old now?) textures and recipes back, or wait until tomorrow.
Now, these changes are by no means what IndustrialCraft is now going back to. As I was asked today, the IC2_lf branch has not been accidentally merged into the Experimental one. In fact, by the end of today even build 73 will revert back to the normal Experimental settings. Things placed during the period will retain their settings, a tier 2 MFE for example will stay tier 2 despite all newly placed ones being tier 3. This is not a new end for an old concept however, far from it in fact. This is the demonstration of a new profile system that is being conceived.
It is impossible to be sure people will like the more crafting heavy set of recipes Experimental hold. Or that they even want everything modern IndustrialCraft has to offer, it is after all substantially bigger than even IndustrialCraft², let alone the original IndustrialCraft. Thus we will be offering the option to not have to use them. By default there will be the profile that has everything associated with the modern IndustrialCraft² Experimental, which will function like the builds you can download now. But there will also be a second profile, a classic one offering as true to life IndustrialCraft² experience as can be achieved within limits such as performance constraints and minor modern tweaks, like improved coloured cable placement and the removal of wrench loss. This shan't be the only offerings either, in an ideal world it will be possible to create your own profiles to match your own tastes, such as a Classic that uses Experimental textures or an Experimental that only has EU machines. Such creation would be possible within an extensive visual ingame-config, and be possible to import and export to allow others to use your settings. Switching between profiles would be as simple as picking one and restarting the game. Cross-profile world compatibility is still up in the air, as whilst currently it is (April Fool's jokes ruining worlds isn't cool), that also provides limitations to what can be done especially regarding true Classic accuracy. Any feedback regarding this or any of the concept is welcome.
Whilst this is still some weeks away from being fleshed out further, hopefully it provides some idea into what the current train of thought is regarding abstract direction and some potential ideas for future usages of IndustrialCraft. As a final note, Advanced Solars is coming very soon (hopefully it is more obvious where my time can be taken) with Advanced Machines and Gravisuite following as closely after as can be managed. Apologies for the rather large wall of text, but I felt it better to "fully" explain everything given people are probably coming at this from different initial understandings.