The one good thing to have come out of Blockstream is the confidential values technique for blinding output amounts.

They hide only the mantissa part of the number and take 2.5KB to achieve that.

My confidential values technique hides the whole number in 0.4KB (subject to ongoing peer review, positive so far).

https://bitcointalk.org/index.php?topic=1085436.msg11597427#msg11597427

Can confidential values be implemented without a sidechain/directly on the mainchain?

Yes.