I can't speak for a global community, but I will say there was a group I played with where we mixed Advanced 2e, 3.5e, and 4e in all our games and it worked well. It is important, I think, that you pick the system that most suits you and use that for a base. This gives you a solid starting point around which to build your ideas, as you know what your basic dice, combat, magic and movement systems are going to be. Then look at the rules and what you would like to incorporate or change from that perspective. Be careful with direct conversions for health and damage as they rarely translate well without modification to the new system. For movement, obviously just convert units and round. The rest of it (magic, magic items, additional systems, etc.) will most likely suggest direct conversions themselves, and often can be brought in with little or no modification.
Balance is key as mentioned elsewhere. For example, healing surges in 4e are a "player only" thing.... except they aren't. Among other compensations, monsters have more HP to deal with this set back. That said, it is a great example of a system that can easily be added without much hassle. The system is well established as a percentage of HP so the only hypothetical work is figuring out if you want to keep it once an encounter (and why mess with a good thing?)
I would suggest you playtest all your new rules in small batches. Introducing large modifications all at one time may lead to issues. Likewise, before discarding a new rule outright, you may want to try modified forms of it first before you decide it doesn't fit your game or play style. Also be aware that new rules will be hardest on the DM as the person juggling the construction of the game. The DM is the one who ultimately has to patch over any issues with the ruleset being used.
Finally, while it's most likely you do, having a good knowledge of each of the systems your incorporating is very important, in my opinion. Not that you can't incorporate anything you want, but new rules seem to integrate smoother in my experience if you incoporate the things from the games you have the most depth of knowledge about. So start with those unless there is a real desire for a particular rule change. We had several experienced 2e, 3e and 3.5e players in our group, so it helped inform our decisions immensely when selecting ideas to augment our game. This is especially true if you ever decide to crib from non-DnD systems.
And if you care to know, we augmented the 4e ruleset with 2e and 3e, however, you should pick whichever one you like. It just so happened we had a lot of people wanting to play 4e because it was the brand new thing at the time.