Zoho Creator is probably the closest thing to a web-based Access product that I've seen, and it's still not quite Access. Access occupied a very strange space in between an actual application framework, a database GUI, and an IDE.
I personally would not want to be responsible for security for a web-based Access clone. Enormous attack surface area.
But I think Access is awesome for making and battle-testing prototypes that can eventually become actual CRUD apps. Great intermediate step somewhere in-between e-mailing spreadsheets and building a Rails app, for getting shit done at the office.
Agree 100% on this. To truly replicate Access online, you'll have to provide some sort of scripting interface that is moderately performant. Seems like a complete nightmare.