Some time ago, I read somewhere on this forum that a SegWit (or SepSig if you prefer) hard fork would be cleaner than a SegWit soft fork. I believe the same post implied that the soft fork technically took advantage of a potential vulnerability that should be closed. IIRC, the same post indicated that closing that potential vulnerability would require a hard fork. Now the article link posted at
https://bitcointalk.org/index.php?topic=1343346.0 indicates that the core team is planning on hard forking to 2-4-8 in addition to soft forking to SegWit. Given that last point, why on earth wouldn't we just add SegWit, close the potential vulnerability, and include the 2-4-8 change all in the same hard fork?