I actually think this would be a good idea: kind 51.
nostr:nevent1qqsp43nzg6r2zyts2kpchwsf09cragshhnu7vs7weyauhtfwjdu24acppemhxue69uhkummn9ekx7mp0qyghwumn8ghj7mn0wd68ytnhd9hx2tcpzdmhxue69uhk7enxvd5xz6tw9ec82c308s5t3d
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Whatever starts the ball rolling in getting away from using kind 1 for replies.
You can't "get away" from anything.
Clients still have to support "old" Nostr standards because old notes will still exist.