There will be 2 scenario if we apply this (or maybe more),
1. Lets say "User A" create a topic and want to earn merit, so he create a lot of account and reply on his own thread to earn merit.
2. He can try to start bounty and pay user to reply his thread. So, he can earn merit.

I maybe wrong, but from what i see from thread that have a lot pages, some of them are reply the same answer again and again (well, not all thread) and some of user probably doing copy-paste or plagiarism. So, this is not good idea, sorry.