I would simply love to see a PD skill for crossbows (Power pull), which would affect a lot reload speed of the weapon. Give in exchange low reload speed for crossbows, which would be corrected with high PP skill. Then, STR crossbow builds would be effective, and people having low PP skill be penalized a bit on reload, since they got 180 wpf in crossbow (max accuracy).
I love the idea of some type of skill sink for xbows to help balance, but if you aren't careful you will further skew internal balance of the class as a whole.
A skill like PD would be an awesome idea, however it should have positive and negative effects so that increasing the skill won't simply buff your class but also negate the buff in certain situations. This would increase variation in builds amongst the crossbow playstyles.
Every Crossbow should be effected by a skill like PD but not require it to use. This would allow use without any investment but pure builds would be vastly more effective in its use. Of course you would need to nerf Crossbow stats across the board by 20% or so to negate the damage increase of PD effects and add greater deviation between pure/hybrid/no investment.
PD it self should do two things to Crossbows - as PD skill increases damage increases, and reload time increases as well. Think about it; The more punch it packs the longer it should take to ready up. By doing this you effectively have two choices as for min-maxing would only grant you so many benefits- as there would be a happy medium.
If PD increased damage by 14% per level it should increase reload time by 14% per level. Lets not over do it... cap PD effects on xbows at 6; so (6*14)(-.20)= 64% damage increase at 6 PD investment but also a 64% increase in reload speed so it would take longer to reload. I also believe that the first 120 WPF invested in the crossbow skill should do less than the last 30-40 invested to further the gaps in the issues of zero investment. With this system you would need 3 PD at the very least to negate the -20% damage debuff along with these changes.
The exact percents I gave as an example probably wouldn't work but its just a rough idea.
Reload speed should be a direct reflection of a more powerful crossbow; the more kick it gives the more time it should take to be ready to fire again.
as for the original suggestion in this thread of making arbalest 3 slots; I believe this would destroy whats left of an already dying breed.
TL:DR version ; Purple.