Hai! Sorry for not talking for years. If you remember me lol
Anyway, do you think SpongeBob would make a good "Batman Beyond" equivalent to Mermaid Man?
Hiiii!! Of course I remember you, I don't forget anyone silly <3
Anyways I think it would be an interesting idea if they did a Mermaid Man Beyond in Spongebob. Though I imagine Sponge and Pat may react to it similarly to how they did to Captain Quasar The Next Iteration (if you've ever seen that episode).
Though this does remind me, Captain Quasar and The Snail Fail and Sir Urchin show are both in universe shows that exist as a sort of replacement for Mermaid Man and Barnacle Boy (because their voice actors have, you know, passed on). I like both of them but they don't quite cover the appeal MM&BB had (though I wish they used Snail Fail and Sir Urchin more often, I think they're cute).
The franchise has tried many ways of getting around this issue such as MM&BB showing up in the background with no dialogue or them conveniently being cyrogenically frozen in another. There is the Patrick Star Show which takes place in the past so they just use a young in their prime MM&BB so they already had different voice actors for their younger counterparts. There is also a pets version (akin to Krypto the super dog) called Mermaid Worm and Barnacle Barnacle. I quite liked that. Also their vampire squid villain is such a baddie
I remember getting into a discussion about this and the possibility of the old age MM&BB getting replacement voice actors. It could happen as they have replaced voice actors for many characters already (dirty bubble, manray, etc). It could work. I mean there is Patrick's voice actor who did Mermaid Man's voice for Spongebob's Mermaid Man themed alarm clock once so we know there are people who can mimick the voice very closely. It's at the very beginning here.
I remember reading years ago about something something them not wanting to replace the voice actors after they passed out of respect but its been so long I don't remember where I read it and I can't verify the source. Don't use this, I don't want to create another "Hillenburg didn't want spinoffs" type situation.
But if that really was the case, then I do think doing a Batman Beyond type situation would work very well. In fact, in the spongebob comics, there is lore to back up this idea. With each previous Mermaid Man retiring once they get too old, and a young Mermaid Man to take up the title, with our Mermaid Man being amongst a long linage of Mermaid Men.
That way you don't have sponge larpers complain about them changing the show and lore and disrespecting Hillenburg stuff. Just hit em with the official comics lol