As it is now, flamers were something that I did have in my lists, but really only in my Imperial Guard lists. There they were very easy to get into the list and did their job for a very small point cost. With some of these rules changes, I see flamers changing the game.
The flamer could very easily turn certain units into real defensive anti assault units. It would bring a new definition to the idea of the bubble wrap. IG units with tons of flamers in them could be very hard to assault in mass.
Lets look at some of the rules rumored to be coming
A unit being charged gets to shoot (pistols, rapid fire, and assault weapons) at BS1. Flamers if allowed to use snapfire will be the defensive weapon of choice. No need to roll, just hit a ton of models preparing to assault you. This would also make the enemy units have to carefully choose where they are going to attempt to assault you (hopefully to not get flamed to death before the assault)
Setting Terrain on Fire:
This is huge. Take a simple look at Grey Knight Interceptor Squad. 30" of movement, followed by two Incinerators. Add to that the chance of setting that terrain on fire, and we have some serious devastation caused by a super fast moving unit that could be anywhere on the board it chooses.
Templates hitting models:
This rumor is very vague and borderlines wish listing, but it something to mention briefly. This, combined with snapfire, could be devastating as models move into position for assaulting. I believe we would still see the requirement for hitting the most models under the template if this rule does indeed come into 6th.
Over all flamers are very cheap compared to the cost of heavy weapons. Not to mention that there are some nasty flamers out there. There are many people that just do not field flamers, could they be the new meta for 6th edition?