Thank you for this OP. Severely limited in terms of technical knowledge here, but always keen to follow Bitcoin upgrades and have been happily using SW for a while now, enjoying the very obvious benefits. Just curious from the paper, which assumes (as I do) that SegWit has already reached the stage of significant adoption (at least through P2SH) and can be considered mature, yet the percentage of legacy users and services still stubbornly holding on. Will implementing this and possible further expansions cause even further risk of alienating legacy?

I know it doesn't affect them (no network partitioning as your paper says) but the fact that they can't transact/spend to native SW unless using the same client already must mean some users are shorn off... Or does it actually make no difference, or would it actually further push to encourage SW upgrade?