Due to Belmont likely taking longer, this won't be entirely true on the Mass Central Rail Trail, at least. Belmont's Phase 2 is fully funded but currently for 2025-26 construction. It could get moved up due to other projects being delayed, or like the Bedford towns refusal to pave the (already funded) Reformatory Branch Trail. Belmont's Phase 1 (the western section, actually) is still in the 25% design phase.

Yes, precisely this. It was brought up during the initial engineering outreach at the 25% design and they stated "We have learned since building the Minutemen how to design for speed and safety."

The Minutemen is a joy to ride because it doesn't have anything like this, of course, but it's also why there are more high speed (relatively) crashes both with cyclists and vehicles at street crossings.