I have recently switched from flask + psycopg to sanic + asyncpg for my http APIs. I'm pretty happy with the results and the transition was pretty smooth, it only took a day each to switch out each and go from fully synchronis to fully asynchronous.
I'm considering switching from Flask to Sanic, but I worry about Sanic's ecosystem. For example, I'm using these Flask plugins: Flask-Cache, Flask-Compress, Flask-DebugToolbar, Flask-DebugToolbar-LineProfilerPanel, Flask-Login, Flask-WTF.