I got back out there to investigate the extension but decided to start in South Yarmouth. I got to end of the extension where it becomes a dirt trail parallel to the power line. I stopped for a big snack & a couple wearing enormous inflatable tubes, walked by coming from Duck Pond. they said "you're almost there!" but I had to ride back on the road bike. I might just return w/ an MTB & tool around. I've seen some double & single tracks out there that I haven't been on w/ a bike & some I haven't ever been on
if anyone needs a cure for insomnia ...
used "find my phone" feature to provide my location at the end. the blue dot is me. the diagonal pale green trail next to the blue dot, is the power lines. the trail I'm on is to the immediate left of & parallel to the power lines

& looks like this

the extension itself is so nice

minor exceptions

look forward to riding it again!