I'm also in the same boat for buying the Panasonic ub820 one of the best 4k player, but just waiting for availability in India first rather than buying from Amazon US due to the voltage issue, will be needing a step down converter.
Wrt, region lock... The 4k Blu-ray's are released region free and only few of the 2k ones are released region coded depending on the region of release. In this case 2k Blu-ray's other than region coded 'A' will not play in the US version. So yes Indian released Blu-rays only with region code C or B will be not play. I've numerous Blu-ray's bought from India which are mostly with region ABC or BC or only C.
But there is a trick by updating the firmware of Panasonic Blu-ray players as I had did for my super-duper 2k player BDT220 almost a decade back. The same is available for 4k too.
Now I'm only buying from the US, though it costs a little more due to customs duty but still I get the best intended quality as the release, and anyways in India Blu-ray's are not released anymore of what I've the knowledge.