That's already in Soldat's Flamer. But that + the fact that the number of flames that can be stuck onto a body is infinite makes the game very laggy...
I'd rather the Flamer be like this:
1. Flame touches player
2. Player takes damage of 1 flame
3. A second flame touches player
4. Player is seen with only 1 flame, but the damage is increased and the duration of the flame is increased.
Yes, it's like the current Flamer, but instead of having multiple flames stick onto someone which is the ctual source of the lag, there will only be one flame sticking but the damage and duration of that single flame is increased if more flames touch that enemy.
I think that may solve the problem of lagginess with Flamers, especially with lots of players.