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Another question, "Would high fees (caused by usage of Ordinals and other similar protocol) lead to decreased usage of Bitcoin on another aspect (buy goods, paid for service, etc.)?"
It would definitely lead to decreased usage of Bitcoin for financial transactions onchain, which could be pushed offchain, leaving Ordinals users the more willing onchain participants to pay for the high fees that the miners require to secure the network.Another question, "Would high fees (caused by usage of Ordinals and other similar protocol) lead to decreased usage of Bitcoin on another aspect (buy goods, paid for service, etc.)?"
But would people move to off-chain when they know to open/close LN you need to create on-chain transaction? In addition, would people use off-chain if they only make financial transaction on few occasion (e.g. buy gift card or pay website domain every 1 year)?
if they come up with a way to throw away all the X oldest blocks periodically then that could guarantee the blockchain never gets bigger than a certain size and then you could have block sizes as big as you wanted. 
That doesn't sound good, but you can have a look at MimbleWimble.Could you elaborate further? I know it used to combine many unconfirmed TX into one big TX, but i don't see how it could be used to discard or reduce size of old block.