All right I've been thinking
So to begin I will try to make this suggestion as realistic as possible. I know something about programming, so I will try to come up with things that are possible to program. Also I will be combining some stuff from buildcraft here, because I think it is very good to use it with industrial craft. On the other side I will not make this dependable on buildcraft. This will also work without it as well.
The first biggest problem with PvP is the fast mining. You can mine everything and everywhere in the matter of seconds or minutes. Why would anyone build a fortress, when everyone can just mine his way inside and steal your stuff or sabotage it. The solution to this: make mining times for everyting very long maybe like 15 seconds or more. Now you probably think: but wait this will suck. I wont mine 30 minutes just to build a small house. Well you are right it will suck from the begining, but think about it you are playing industrial craft. Mining is not a job for you. Let the machines do that. The best way to start would be to make a house in a cave entrance. When you have enough resources, you can build a quarry or a miner with a scanner that will make it mine like a small quarry. Miner or quarry will mine resources the same way as usual, so it will be important to have one.
The other problem is building. When everything takes long to mine, you will always find some idiot that will want to spam blocks to block your way. The solution to this is: When you spawn a block, it will be like a construction foam. You will be able too see trough it and walk through it. You will be able to destroy it with one hit. After some time (30 seconds maybe) the block will solidify.
How the gameplay will look like:
When you start you will mine sume wood as usual, and you will make some stone tools. Then you will search for a cave. When you find it, you will make a small house there and then you will go to explore the cave. If you dont want to have a base in the cave you can make a wooden house. It won't be durable, but it may be better for somebody. In the caves you will mine some resources and you will start to make some basic machines. Later, when you have enough resources you will build a miner or a quarry. From there you can start building your own coble/stone fortress. I suggest to keep your resources hidden and well protected, because there will be a lot of people trying to steal them. Remeber even the coblestone will be a valuable resource. Tesla coils will be great to protect your resources, because people won't just mine around them. For mining rooms underground it would be good to use a filler from buildcraft. That reminded me that TNT should be a bit nerfed, but also you can use dynamite to mine things. But don't make dynamite too overpowered wee don't want people blasting their way into your fortress. Reinforced stone should also be very very durable. You will be able to destroy it with some high tech weapons but you won't drill through it like it was a butter.
For this mod it would be great to make some protection systems like sentries and better weapons. On the other side some offensive system that you can use to destroy them or to
switch them off etc..
-Mining time for almost all blocks increased rapidly. Ores and wood related blocks mining times will increase only slightly.
-When building blocks the blocks will first appear as a ghost. They will solidify after about 30 seconds.
-Ghost blocks are very easy to destroy you just punch them.
-New scanner for miner that will make it mine even the stone so it will act like a quarry. Its mining speed will be unchanged.
-Alarm - New item will start to beep when radar detects something
-Radar a block that will send a singnal to Alarm when somebody is nearby
-Reinforce stone is now impossible to destroy with a pickaxe. You can drill through it with a diamond drill, but it will take a long time.
-Molecular decomposer field generator (temporary name ) - Block that will decrease the mining times of the blocks in the field, so you can rebuild your base.
-Nuke is now very hard to make and costs a fortune.
-New laser defense turrets and guns from Alblakas weapon update. (we will see what he will make )
There could also be several teamplay gamemods. For now I can think of 2.
The first one would be something like mine4dead. Each team will have a block and the other team has to destroy it. You could power the block with EUs to shield it with force field etc...
The other one would be like mining some rare resource and bringing it to your base. The resource would spawn in some area, and it would be respawning there, so the team will have to take control over that area. Or it can spawn randomly (imagine it falling like a meteor) and the team will have to make a detector to detect the place of the impact. You will have to power it with EU of course.
Well tell me what you think about this PvP solution. I know it is a bit hardcore, but when you make some machines it won't be that hard.
P.S. Forgive me my grammar mistakes. THX