I know the subject of armored suits are subject to heavy debate by this forum, but I like to add my own flavor of suggestion to help people find the thin line between genius and crazy.
Anywho, I propose an alternate upgrade path for armored suit wearers. A lot of progress has been made with the implementation of the Hazmat suit, which is an environmental rather than combat suit. The Nanosuit, a rechargeable combat suit, provides little environmental protection aside from fall damage protection (which it provides at a heavy cost). The only available upgrade for this suit is the Quantum Suit, a supposed end-all, be-all suit that provides both environmental and combat features as well as a HEFTY cost.
Why not add a suit that provides more FEATURES rather than COMBAT EFFECTIVENESS, and do it at a lower cost to the player? The reason the QSuit is expensive is because it provides effective invulnerability for fairly long periods of time. The Hazmat suit is almost dirt cheap because it provides little physical protection from enemies (it's made almost entirely of renewables).
So now we get to the crux of my post: the alternate path(s):
-The Energy Suit.
Remember Isaac's suit in Dead Space? How would you like that suit in Minecraft? A nice glowing tube on the back of what seems at first glance to be a Nanosuit. This suit taps into whatever 2nd-tier energy sources you have in your inventory, and allows you to use them to power your tools. Energy Crystals, BatPacks, Lappacks, they can all be used straight out of your inventory. This ability can even be toggled on and off in case you just want an armored suit. There is a drawback to this - that neat glowing tube on your back is a weakness! Explosions, projectiles, and physical attacks from behind will do additional damage to you.
-The Infiltration Suit.
This suit is pretty simple. It's a lightweight suit built up from a Hazmat suit, reinforced with carbon fiber plates a la nanosuit. In addition to providing compressed air underwater breathing, fire resistance, and fall damage resistance, the suit also has a toggleable invisibility functionality similar to the invisibility potion. The advantage is that the suit is also invisible while stealthed, whereas you must be naked to use the invisibility potion! Items held in your hand will still be visible, however. The Stealth functionality is fairly energy-expensive, but it can use Energy Crystals kept in your inventory. This suit could also be merged with Nightvision Goggles, whenever those get implemented.
-The Camouflage Suit, A.k.a. the "I'll-never-look-at-a-creeper-the-same-way-ever-again", or "The TF2 Spy".
Instead of this suit providing invisibility, it changes you appearance (along with hiding your name). You can choose from a variety of (reasonably-sized) mobs, or on SMP you can select the appearance (and name) of any player on the server (except OP's, unless they are OP as well). This suit would be much more stable than the infiltration suit, due to the entire suit power grid focusing on micro-projection. This could be incredibly fun for sneaking or goofing around, since many players are expecting certain behaviors from mobs.
-The Detection Suit, A.k.a. "The High Tech".
This is a suit with advanced electronics in the helmet to provide special functions such as object tracking, target identification (yes, it would work through the Camo suit and Infiltration suit, but regular mechanics would still apply), reticles encircling potential targets. This suit would also have additional modes for sight, including night-vision and thermal-vision. Unlike the other suits, the Detection suit only provides a minor armor improvement over plain Nano armor. The suit would also be visually striking and easy to identify in a battle. The main feature would be object tracking & lock-on. The lock-on system would function much like auto-aim, when you aim it would compensate for your & your enemies' movements, so if you for instance fired a mining laser at them, if they maintained current trajectory, it would nail em right in the chest.
(How could I not have thought of this one sooner??)
-The Rocket Suit.
This guy is much like the Qsuit, but instead of providing quantum jumping, it provides :Electric Jetpack: (Quantum?) jetpack-ing. The jetpack function would be significantly more expensive than the electric jetpack, since the jetpack had to be integrated into a form-fitting suit. Additionally, the suit does not provide 100% invulnerability like the Qsuit, but it does provide a very high quality protection.
P.S. - I would like to see this implemented because it would provide for some unique new experiences in Minecraft, especially in SMP.