It seems like TMD hosting supports Memcache instance. Is there a way to make chevereto use Memcache instance?
In my opinion OPCache is simpler because it basically caches any given code / file and is has been tested by caching language strings with very good results in Chevereto. Having said that, the only missing caches could be user settings, website settings, etc. But all those can be made in files so the server does all the cache stuff automatically because you do a file based cache (that on top of that gets OPCache).
The only stuff where you can get an advantage by using Memcache is in MySQL cache for things like listings or data like that but those performs so fast that for now we don't need to cache that. Also, mysql as his own internal cache that works right out of the box.
The above code won't work because settings variable doesn't handle session handler.$settings['session.save_handler'] = 'memcached';
$settings['session.save_path'] = '127.0.0.1:11211';