Thanks for the excellent feedback everyone -- I'm still not sure which path to take but the info here is much more than I had before and gives some framework for making a decision.
I am initially tempted to just go with the truck approach and have the water cleaned using reverse osmosis service once/year, or when CH levels get too high, but we're a salt pool....and it appears I'd have to complete replace the salt in the pool after every cleaning which would also involve shutting down the SWG temporarily and then ensuring that after reactivation that the pool chemistry and SWG are returning to good states. Perhaps that is the right solution but not as simple as it first appears and will take a lot of salt.
Our pool is covered (automatic safety) so I wouldn't expect much need to top off daily using the auto fill, but yeah will still have some evaporation and splash out. I'll considering putting in a water softener if the pool builder says its OK, but its unclear how large of a unit we would need and it does seem that would take up some significant additional space and require its own maintenance. I'd probably set it on a low setting to ensure any changes take place over a long time...but the risk of a misconfiguration or lack of monitoring causing severe problems to an expensive pebble sheen/etc is also something to take into account, plus the up front cost and ongoing supplies.
If the trade offs are equal, it might make sense to just go with the RO approach, basically -- we'd shut down the pool for major maintenance for one week/year which is probably not that bad honestly. Plus, no additional plumbing or equipment space/general maintenance complications. I assume the RO truck guys would verify that the resulting calcium levels were just above 200. I might need to readd some other chemicals/borates/cya too, I guess...I can handle all that as long as we're not talking about a month to re-stabilize the pool chemistry.
