effects of regulation is no longer a guess because it has already happened on a large scale. before when bitcoin was not regulated in any country you could only guess that such as such may happen if it someday became regulated. but ever since Japan regulated bitcoin we have a real life example.
here are the results:
1. huge adoption by investors
2. huge adoption by different merchants
3. with removal of taxes the adoption by merchants grew even more
4. finally the price went up from $1000 to $4000 (although most of it was because of scaling and SegWit but Japan was very effective also).