ok, had some time to test this:
unfortunately, on both commit versions:
disconnect();don't do anything. they return 1 (success) as long as the slot is in range (if the slot is out of range, the program segfaults when running) you can set port number to whatever you like well out of the port range for the corresponding plugin and it will still give you a 1
more importantly, if you set meaningful values, neither connect nor disconnect have any effect on the chain. i tested this with a render.cpp that is working fine with the "old" LV2Host.cpp and amended the connect and disconnect functions to test, but i guess that should work. the program runs fine (see above for caveat) but the functions have no effect.
bypass(); function works as intended, it takes the plugin out of the chain and the sound does not come through anymore. also cpu usage drops which got me all excited :-) but, since connect does nothing, i can't put the signal back into the running chain...