Hi,
As I know an upgrade to Helix Ultimate is not planned, as you noticed we mostly develop new templates on HU.
It's a very time-consuming process, and if helix3 works, no need.
Useful tip:
1) Make site backup
2) Recover site on test subdomain
3) Install Helix Ultimate template, set as default
4) Assign Glamur for selected pages only
5) Using custom.css from HU add styles which you liked from Glamour, of course, first use Code Inspector to be sure that they are OK
It should take you a few hours to make a very similar look.