Hm, wonder what would happen if entry hazards suddenly turned mutually exclusive? Placing one would rid your side of the previous ones? At least in Doubles, you could come across people who target their own teammates with Spikes to get rid of the Stealth Bug (hey, we're being hypothetical!) the opponent placed there.
It would also open up for more flavours of hazards. Hazards would eventually be overpowered if you were allowed to stack them endlessly, and GameFreak should be aware of this. If they ever want to make more entry hazards, they will have to limit their stackability sooner or later. As long as you can stack them, there's a limit to how many different hazards you can have in the game, or they become overpowered. On the other hand, all the bigger waste when your opponents finally Spin them away. However, adding diversity and power to a tactic that only has a single counter wouldn't be very smart, balance-wise. Thus, any further buffs to hazards would also require new or more reliable ways to remove them.
Logically, we're down to four options:
1. GameFreak will not add more entry hazards in the future, making us play with them just like we currently do.
2. More hazards to play with, but also a buff to removing them, to prevent overpowering.
3. More hazards, but also a change in entry hazard mechanics to prevent overpowering (limits to how many different hazards can be placed, or similar), but the ways to remove them stays the same.
4. More hazards, but no further counters, making the strategy more powerful.
I, for one, would love to see temporary hazards once in the future. Say, glowing hot coals that would cause burns (or cause Fire damage ŕ la Stealth Rock) if the opponent switched the next turn (or the next two, but certainly not longer), but cool after that and become useless. A sort of "partial trapping" move. You'd be allowed to switch to your heart's content, but it would come at a cost. Bonus points for strategies involving switching to Guts abusers, and counter-strategies including Pursuit or anti-Guts-user moves on hazard setters.