Why?

Becuase for it to be effective, your client must connect to only that one relay exclusively. Otherwise you get and send all length of notes.

And only <= 140 go in, so that doesn’t matter

It could be usefull and effective if several relays were configured to only allow 140char and special clients were designed to exclusively connect to those relays. Then you'd have a true 140char application.

All you’d need is the ability for a client to add ability to filter to specific views or modes to only use certain relays. For example, create a Twitter mode which only shows and posts notes to 140 char relays (you tell the client which relays are 140 char relays) I think @jb55 is working on this already with Damus and filters. Not 100% for sure tho.

"Mode" is perfect innovative solution albeit complicated.

You could have a single client, tailored to the specific modes you care about: - Twitter (140 chars) - Medium (long form) - Instagram (images only) I’m sure there are cool things you could do if you were able to customize both the event kinds, relays, etc.

Not sure. But I think @pinstr #pinstr does that. I can't use many options for technical limitations.