You answered your own question.  Lighting, custodians, fedminits, stuff not yet invented is what will happen when it’s $100 equivalent per transaction. 

Normal people already hold checking, savings, credit cards, brokerages, HSA, Venmo, etc accounts. In the future they could mix a custodian lighting wallet for checking, a custodian L1 / Fedimint / whatever for short term savings, and cold storage self custody for retirement. 1 solution should not meet all of these needs as they are different. 

Necessity breeds invention. Bitcoin already transacts as much as Fedwire and its open nature means it should be easier to verify your funds with a custodian than the current black box of fractional reserve banking. Not saying it shouldn’t ever change, but the barriers being so high is a good thing. It means there needs to be a real problem to solve instead of hypotheticals in the future. 

 I'm not trying to argue, just verifying the trade-offs wth a back of the envelope calculation. 

The goal is to maximise participation in running nodes, but there is not much point running a node if you can't afford a transaction. 

The block size means there are a maximum of 4000 transactions every 10 min. That's 210,240,000 transactions a year with full blocks. 

Even if you saved up to add to or withdraw from your retirement savings once every 10 years it only allows 2 billion people to use Bitcoin onchain. What are the other 5 billion meant to do? 

I'm not arguing for larger blocks. It's an inefficient scaling solution and one that is not beneficial for a long time. We should develop the scaling solutions cautiously first, because these could become more different to implement as time goes on.