Fully decentralized miners is a thing that would really help with all the concerns. Faster and cheaper transactions are something that would make bitcoin even better and more popular. Something that makes bitcoin 100% anonymoys, not pseudonymous anymore.
I'd say those are the 3 things are the ones that would make bitcoin a "perfect cryptocurrency"
Also some integration of Ethereum technology could be good for bitcoin.
i agree you need always to change the algo to have a fully decentralized coins, that can't be taken down by asic, then you have cheap transaction, this is tricky because of the block limit, and block halving, if the halving was removed fee would not be necessary isn't this true? this system would still be limited and not inflationary, just that at some point the reward go to zero and from there the fee kick in, not from the beginning like it is now