I believe that this tag should be added to improve compatibility from other mods. This can be easily solved by just adding the #tfc:seeds tag to the #forge:seeds tag. Forge also gives vanilla seeds the tags for them based on the different type (e.g., #forge:seeds/wheat) which other mods respect and do the same, which is something to consider.

This can be added via a datapack, "improve compatibility with other mods" is meaningless without an explicit purpose or convention. In similar cases we have elected not to use tags because the items aren't functionally similar (TFC wheat and vanilla wheat seeds are not functionally interchangeable, and it doesn't make sense to tag them as such). If there's a good justification for why this tag adds more benefit than detriment I'd consider it.

I understand the hesitancy but I have added the forge:seeds tag (not the derivatives like forge:seeds/wheat, etc, because I wasn't sure if it would mess with anything else like you mentioned) and there wasn't really any changes that didn't make sense in the realm of TFC. If you're wondering what exactly I mean in terms of compatibility, these are just some of the things that I have noticed:

• quark uses forge:seeds to determine what can go into a seed pouch (bundle for seeds)
• sounds uses forge:seeds (and other tags) to determine what sounds should be played when moving/selecting items
• create crafts and additions and ars nouveau use forge:seeds in recipes (where yes it does make sense that any seed including ones from TFC could be used)

There are likely other mods that use this tag in a meaningful way but this is just what I have noticed, and I haven't noticed any instance in an >100 mod modpack where adding this tag had any effects that broke/interfered with any functionality in TFC.