Take Bytecoin right now. Their blockchain is over 9 gigs to download. How big will it be in 20 or 30 years? (assuming its still around). What solutions are going to be in place for people to download and store such a massive file?
Now pretend you have 20-30 different coins all with massive blockchains.
yes it's inconvenient but that surely can be easily sorted out. Perhaps some cloud based services for this kind of storage but with proper safety infrastructure would do.