What you are proposing would severely undermine VIA's efforts of fleet standardization - for benefits which would only materialize in the second half of their usefulness (if ever). I really hope that we will see the day where VIA's Corridor operations become so extensive that having two separate fleets becomes a suitable solution, but we unfortunately are a long way away from that point...
One size does not fit all, and if you try you end up with something that is not very good in all of its applications. A compromise.
The Avelias absolutely would immediately materialize their usefulness, just like they have on the NEC, even though the majority of the NEC is not rated for HSR: they tilt further than any other north American train has done before, more so than the previous Acelas by Bombardier. Because of this they were able to shave 30 minutes off the Acela route. Thats huge.
Then, you have the added benefit of HSR ready trains when the decision is made to upgrade. Portions that are straight already, like the track from Ottawa to Montreal could be upgraded to HSR standards first, and the time lost in the curvy Havlock section can be "caught up".