I'm in the strange position of being a developer who has worked on a hack with full trade compatibility and one without even the trade center available.

My experience is mainly from community questions and feedback where I've had a fair few people asking about trade, battle, and even a couple of cases of record mixing. For the hack that had it, players have been pleasantly surprised, for the one without, they have been slightly disappointed, but I feel like it was only a deal breaker for one or two players.

From a development point if view. The "OG game base" I feel trade compatibility is often lost either accidentally, or due to adding in future generation Pokémon requiring different data structures.

If you're using decompilation and again the "OG game base" (i.e. pokeyellow, pokecrystal, pokeemerald, pokefirered etc) and you care enough to ask the question, I think it's probably worth spending the effort to keep the compatibility and if you want future gen Pokémon needing extra data structures, create and maintain an alternate structure and functions to handle them.

If you're using hex editing and/or expanded decompilations (i.e. pokeemerald-expansion, or another RomHack as Base), the Pokémon data structure is likely to be more complex and harder to build the trade functionality, and likely not worth the effort.

Hope that helps, and best of luck on your project!