Light rail from UTC to the intersection of El Camino Real and Del Mar Heights is another ~5 miles, probably longer since the terrain isn’t flat. Connecting to the coast line and running on existing tracks, then up Del Mar Heights isn’t an option due to the grades involved (unless one wants a light rail cog railway!).
That’s almost half the length of the existing 11 mile extension. Who will pay for it and deal with environmental/NIMBY issues?
What about a station on the existing main coast line at Del Mar Heights Road and bus rapid transit east/west along the road? And if we’re dreaming, electrify and double-track the coast line from San Diego to LA while we’re at it and use lightweight electric trains that can accelerate hard between stops to cut schedule times. Right now, the lumbering diesel double-deck dinosaurs that they use are far slower than they need to be.
Temporarily, there could also be bus transit between One Paseo and Sorrento Valley station, maybe down Del Mar Heights to Solana station as well.