Crossbows for bowhunting, in this country, have a stigma attached to them that places them in a totally different situation, quite a bit of difference between compound vertical bows that were introduced 30 years ago at less than 200 fps which have only "progressed" B) to 340 fps in those 30 years, most of that within the last decade. Now, comparing crossbows to that, let's assume a fast crossbow was probably about 330 fps in 2005. Already, with crossbow hunting just now getting on a roll in expansion, a handful of people are already talking about 600 fps crossbows and all the wonderful technology that will bleed over to lowly 350 fps crossbows.

If you think that by virtually doubling existing mainstream hunting crossbow speeds, in a decade for example, will have no negative affect on crossbows' inclusion into archery hunting, you are sadly wrong.
There is already new technology that will allow for 5 lb crossbows with 100 lb draw weight that will shoot in the low 300 fps range but it's obviously frowned upon by existing major manufacturers because they are in their comfort zone with the products they have. That technology has nothing to do with a 600 fps crossbows because the inventors of the technology realize that no matter what happens, a 600 fps crossbow, in the foreseeable future, will be nothing more than a niche product that offers bragging rights but no real advantage over a good 350 fps hunting crossbow, plus many disadvantages, some of which aren't even known yet
Here's what I would guess you can count on with such a crossbow:
Exceptionally heavy
Expensive to buy
Expensive to maintain
Expensive arrows and expensive keeping them in supply (arrow damage)
Expensive high tech targets/arrow stops
Likely limited to hunting only in rifle/gun hunting seasons, if at all
Much more likely to cause injury resulting from a part failure
Much more likely to be severely restricted in some areas, possibly due to being viewed as an assault weapon
.....but I could be wrong