Passport 2 should be the same form factor, the same industrial design, but with further upgraded specs.
Think about it, I would love to see a Z50 coming out but that wouldn't be a Passport any more. Passport is a unique design of a passport size, 3 rows of keyboard, square screen, etc. Changing it would destroy the consistency of Passport serie.
Specs wise however, there are still lots of room for improvement: Octo-core processor, 4K screen, better camera software and hardware, even larger battery by shrinking the footprint of other parts in the phone, etc.
If we allow to change the question a little bit, instead of asking for a Passport 2, asking for the next flagship BlackBerry design, I would say a Z50 at the same form factor as Z30, but much better screen resolution, much better processor, much better camera, the same or better battery life, etc. That would be a dream.