It's such a weird climb.
Gaps would literally be bigger if they put the finish lower
Problem is the only logical places would be at the Basilica, which would turn it into a puncheur 1km stomp finish, or Mirador de la Reina, which would turn it into a 2km stage with all the action coming on La Huesera.
The issue really for Los Lagos is that long stretch from Cangas de Onis to Soto de Cangas and onwards to Covadonga village, which just kills momentum from before.
You
could go from Llomena over Mohandí and even Bada to toughen up that run-in, but you're always going to have to deal with the 15km or so flat between them so unless you make the race hard enough beforehand that it's worth persevering in the valley - like the Euskaltel break of doom in the 2010 Cotobello stage or the famous 2005 Heras stage to Pajáres, momentum is going to be killed in the valley.
Even going over Torno you're going to have the shorter flat from Soto de Cangas, and at the cost of not having any selective climbs close enough to Covadonga to make a difference. Fito or the Llomena-Mohandí doublette is the best you can hope for in that respect.
And unless they pave the eastern path from Següencu to Torio via San Blas, I can't see that happening. That would put a climb of just under 6km at about 9-9,5% at about 30km from the line and cut the pure flat between Soto and Covadonga village to about 6km. But it's a natural park and I don't see them wanting to do it seeing as there's already one road to access the Mirador at Següencu and limited traffic.