I think you hit is spot on with the note on dedicated right-of-way. Once you remove dedicated right-of-way a system becomes only as fast as cars and traffic around. I've been saying it forever that you could throw 900 buses every 1 minute down King George Boulevard and it wouldn't make any difference because they would all be stuck in a giant line behind the car traffic.
Same would happen with BRT. Only solution at the minimum in Surrey on the major routes are right-of-way BRT/LRT or simply dedicated RRT (SkyTrain). My preference would be SkyTrain everywhere but realistically with people in metro-Vancouver geared towards the "if I have a choice all money should go to healthcare and education" and seeing how long Evergreen has taken, you won't see SkyTrain on all 3 routes and it will be SkyTrain down Fraser Highway to Langley and LRT loop from Newton through Surrey Central to Guildford.
My preference though is and will always be SkyTrain extension down Fraser Highway to Langley, and then a SkyTrain loop from Fraser Highway and 152nd down through Guildford along 104th to Surrey Central then up KGB to Newton center. Then from Newton run BRT to/from South Surrey.
Heck you could argue with a SkyTrain loop like I mention, running a BRT up 152nd instead from Fraser Highway give you'd hit more densly populated areas.
Map:
Puple line down Fraser Highway = SkyTrain extension of Expo
Light blue line = New SkyTrain crescent from Fraser Highway/152nd to Guildford (152nd) to Surrey Central (104th) to Newton (KGB)
Orange line = BRT/LRT route 104th, up 128th, down 96th, then up Scott Road to 72nd and up 72nd to Newton Exchange
Pinky route = BRT/LRT from Fraser Highway/152nd to South Surrey/Semiahmoo
Dark Red = BRT/LRT from Newton to Highway 99 P&R to South Surrey/Semiahmoo.
That's my utopian design at this stage. You cover off most of the major centers in Surrey right now bar Cloverdale. Also a SkyTrain crescent in the form of the light blue line would be around 14km which is give or take the length of Canada Line from Richmond-Brighouse to Vancouver Waterfront station so it is a justifyable length for its own line.
It also create 2 new focal transit centers in Newton @ 72nd and KGB, and Fleetwood @ 152nd and Fraser Highway. It also isn't designed such that you're trying to get people to Downtown Vancouver. It gives easy access for people in South Surrey trying to get to Guildford. Or Clayton to South Surrey. Or Langley to Surrey Central. Or Scott Road to Guildford/Surrey Central. Or even Scott Road to South Surrey.
It would allow developers to really push the 'live, work, and play' in Surrey.
Would it be cheap?
Hell no. But makes the most sense to me.
Realistically I think from my map we'll see SkyTrain extension down Fraser Highway first regionally. LRT/BRT down KGB and 104th, probably makes sense in the interim if done right then leading up to a SkyTrain loop. And most likely as a result of that you'd see BRT to South Surrey down KGB first. BRT/LRT down 152nd through Panorama is a few decades out at the speed things move here in metro-Vancouver.
20-30 years and I'd be surprised if our mass transit though in Surrey doesn't look like the map above with maybe the adition of another line from Newton down 64th through Cloverdale to Langley which in essence hits that final Cloverdale area.