Few things I am concerned with about the attribute slots you mentioned, I honestly believe 1 extra, 5 total, attribute slots per item would be enough.  Think about 1 extra stat on each item you have, 8 extra slots in total.  Maybe you could make the 5th slot a special attribute slot, to reduce the chance of an over powered combination of attributes.

I'm with supa on the fact that adding a few extra attributes, and maybe 1-2 more slots wouldn't create much of a need to tweak the current end game content.  Reason being, Titans are still going to be the absolute best gear due to the fact that you cant fab an item that will match up to a titan.

On to the revamped fab windows, they look amazing, great job on that, and I like how simple it seems.  Simple is a relative term, it's not too mind numbingly easy, and it's not the puzzle it used to be.  Well put together and thought out.  Hopefully it'll help simplify fabbing for newer players, and even existing players, giving people an excuse to start their own fabs instead of waiting for the few who have fabs, or have access to a character with fabs.

Overall, personally, I think 1 extra attribute slot would suffice, and the fab revamp looks beautiful, good job.

Quiksilver