If they do not have a suite available for the whole stay but do for, say, the second half of it, offering a guest the choice to move if they want to is good form, isn't it? They don't have to offer, and the guest does not have to accept.

I had this recently on a 3 week stay. I use that hotel regularly and suite upgrades are like hens teeth (only c.3% of rooms are suites). But they came and asked me mid stay if I would like to move for the final week, which I accepted. Had I only been there for 2 or 3.days I probably would have declined. Either way, they didn't have to offer and I had already been upgraded anyway, so it was appreciated.