Assuming the $1.6B allocated for Langley Skytrain is somehow extended to $2B?
Everyone seems to be ignoring that GVRD themselves outlined the L-Line as a critical corridor for rapid transit:
The Metro Vancouver planning is generally more open-ended though, but it's still a critical corridor.
Artubus to UBC is the next logical expansion, considering its (relatively, for this region) high levels of interregional support and benefits, not only to mention that fact that UBC showed significant interest, and would logically help finance it.
None of the other corridors is really on the mayors' or public's minds right now. Note that the Millennium Line extensions were contemplated 2 (or 3, because of the Canada Line) decades ahead in time, what we don't have on the backburner now, isn't hugely likely to proceed.
However, there may be a slot for a ~$1B value 3rd project in the late 2030s, if somewhat optimistically.
Here are my findings for my transit planning map. I'm pretty sure I covered every B-line route currently proposed, plus almost every reasonably proposed Skytrain Route, minus the eastern section of the 95 B-line to SFU (planning on using the WCE and a 2nd gondola to supplement that), and Skytrain to Steveston.
Credit to waves for the calculator, btw.
https://1drv.ms/x/s!AphyHYpEjmp-gpprO8HzjAoyTJgm7Q
Play around with it if you'd like. Note that it excludes the traditional 25% margin on Skytrain projects.