I don't think blockchain size should be such a big issue anymore as disc prices are going down and capacity is going up very fast, so we can expect more people will run full nodes and only this can make Bitcoin more decentralized over time.
But, if the blockchain size is not very large like almost 400 megabyte now, many more people will run it in a way there will be more nodes and decentralization.
Bitcoin blockchain was once small and many people use full node wallet (also because there weren't many SPV wallet), but people switch to SPV wallet when blockchain size getting bigger while resource to run full node (after download whole blockchain) remains similar.
For nodes: Drive's are falling in price, 5g is coming online in a lot of places, starlink and Project Kuiper are going to bring high speed internet to a lot of places. I think once that happens, when you can get a RPi type box with 2 TB of storage you are going to see a lot more project nodes and things come online all over the place.
I partially disagree, you don't need very fast internet connection to run full node. Fast internet connection only needed to let your node download whole blockchain quickly.