What is a softchain? What is softchain and how is it different from drivechain? What are associated tradeoffs and feedback from community?
What is softchain

Softchains: Sidechains as a Soft Fork via Proof-of-Work Fraud Proofs. Decentralized two-way peg sidechain design. Activating new sidechains requires a soft fork, hence the name softchains.
Ruben Somsen shared about a new concept &quot;Softchain&quot; on Twitter and Bitcoin Dev mailing list:
https://web.archive.org/web/20210101153139/https://twitter.com/SomsenRuben/status/1344770107017457664
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-December/018331.html

how is it different from drivechain?

It's similar to drivechains, but without the major downside of having to rely on miners, since all Bitcoin full node users can efficiently validate each sidechain.

What are associated tradeoffs and feedback from community?

You can find few in the replies to the tweet shared above, Paul Sztorc's tweet and below links (mailing list):
ZmnSCPxj: https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-December/018332.html
Sergio Demian Lerner: https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-December/018333.html