This would be a major change and I think over all it's a bad idea but would like some clarification.
First what happens to your chance to proc another hit while moving? Currently I believe you only hit with the offhand while moving 50% of the time right now till you get GTWF. Will you get the full double attack chance while moving with the new change?
Second I'm not sure if it's possible or even how many things stack at this point (like fighter haste boost, monk wind boost, tempest boost, GTWF all on one character for instance) but if you get over 100% chance to proc a second attack.....can you get 3 attacks?
From my perspective it's a fairly significant damage reduction for any build that currently gets GTWF (100% off hand attacks) and has Tempest, Monk stances etc are going to be hit hard.
Other "fun" builds such as monk/rogue acrobat builds may also lose some viability
How about just letting players vote if they would rather keep lag (or work on other fixes to it) then implement these changes? I'd vote for keeping the lag personally.
Make changes like this instead:
1 attack roll for both main and offhand attacks (averaging the two hit if they are different between the two and rounding down). I'd happily sacrifice 1 to hit at most to reduce lag and I'm sure everyone else would do the same way before having these changes implemented to TWF. It would suck for procing effects though since 2 chances to stun with weighted is obviously better then 1 chance, but even so it would STILL be better then the option stated.
I actually really like THF but this is even a nerf to that (which if anything else I would certainly change). Why reduce how well monk stance affects staff fighting? Yeah, I'm one of the few insane people who likes fighting with a staff with my monk, but I make it work. Reducing his attack speed is seriously going to affect his effectiveness though.
This is not a good change according to what you have proposed.
As it is most of us recommend holding off till mid levels before using TWF right now (THF is just more effective). With these proposed changed THF is not just even with TWF it's plain out better. Higher AB, easier to punch through DR, Glancing blows (affects main target as well), additional proc chances on effects, double PA and 1.5 strength bonus.
The only character that would really be better with TWF is possibly a H2H monk at that point (mainly because of full strength bonus to both hands and no insight bonus to attack speed anymore).
Even a tempest ranger would blow compared to a THF ranger!!!
I mean tempest 3 currently gives an extra attack (9 instead of 8)....but with the implied change you would (if I'm reading it right) only get an 85% chance for an offhand attack? Seriously how can you compare that to THF damage anymore?
Heck THF damage might be larger without any THF feats or enhancements!!
Who they heck is going to sacrifice 3-4 of their ranger feats to qualify for Tempest? It will pretty much kill rangers as a class I'm guessing by destroying TWF as a primary combat option.
And without Tempest look at the numbers.
A normal character without tempest but full GTWF would only have a 55% chance to proc offhand attacks (say a fighter). A pure fighter that gets the capstone bonus might pump that up to 65% chance. Compare that to THF damage and there is no way anyone is going to bother with TWF.
Also is fighter capstones double hit proc going to work for two handed weapons as well? You say it and zeal offer a 10% chance to get a double main hand attack so I'm guessing it will affect two handed weapons.
If that is the case, why not do the same for monks insight bonus? Make it also give a chance for an extra MAIN HAND ATTACK so it affects staff attacks as well!!
There has to be a better way to fix lag. Don't nerf a ton of characters and ruin many players builds in the process. Yes we can reincarnate but many of us don't want to and don't want our current characters to no longer be worth playing. Many builds are made around the current mechanics and these changes are too drastic in my opinion.