I'll be doing the same, staying on 56 for quite awhile. This transition has been very poorly managed by Mozilla. I understand the advantages to Quantum but they have left a very large percentage of their extension developers hanging. Web Extensions is not mature enough for many of the large extensions to be ported but despite that they are proceeding with this transition anyhow.
If I was an affected extension developer I would be walking away now. My user base is about to crumble and the best I can do is maybe offer a pale version of my extension in the new system along with a bunch of excuses out of my control. If perhaps WE does get the features I need, why go to the work to re-write? My users will be long gone.
Quantum is great, don't get me wrong. But the new APIs are too immature to be shutting down a huge number of mature extensions and the users that rely on them. It really makes me question the leadership decisions happening at Mozilla in general.