Yes, using newer versions of Electrumx is out of the question and I am looking for an alternative. Currently, electrs seems like a good candidate but I need stuff issues like this https://github.com/romanz/electrs/issues/79 solved!

I need to query a lot of scriptPubKeys are not necessarily mine (like a block explorer). Any suggestions are greatly appreciated! Maybe I will try to get in touch with some block explorers and know owners of electrum servers and ask them what they are using (and if they are using electrumx, what they will switch to).