Saving $ is a good reason, however, google search shows a group 24 battery costs around $95, and a 13 lb odessey PC680 motorcycle battery is around $130. My PC680's have lasted for yrs. Two downsides to moving the battery as you suggest are having to re-wire it, which adds minimal weight back in, but worse, now the battery in the cockpit can become a missile hazard to the driver, which could never happen in the stock location currently dictated in the rules. Batteries are free in the rules, provided they start the car. Buy which ever you want, but I'd be for keeping them in the stock location.
No doubt there's guys using the 88 10.2:1 pistons (not 10.5:1 as you stated). Stock head gasket is 1.1 mm thick. "Repair" gasket is 1.4 mm thick. Some shaving of the head is currently allowed on cars with the 88 pistons, which puts them near the allowed limit of 10.5:1. Even with the .3 mm thicker head gasket, I'm not sure it would make up for the .4 change in the Comp ratio caused by the 10.6:1 piston. I honestly don't know.
When Marcelo's car failed impound at 2016 west champs, he was using 88 pistons with a heavily shaved head, which had just warped, because they had no other at the time. That combo blew well over 11:1 on the whistler test while JP Molnar and Chuck Sharp(?) blew just under 10.5:1 with 88 pistons. Sounds like those 10.6:1 pistons would put engines WELL over 11:1, which would mean many cars would exceed the HP limit, which means changing that rule, which means guys trying to find thicker cyl. heads, yada yada....on the other hand, we could keep the current piston rule, and let guys search out the 88 pistons if they want. BUT, you don't need them to win.