As long as they actually abide by their grandfather clause I don't see any problems with that.
Lifetime licensing (other than as a reward for early adopters) isn't a sustainable business model.
And most consumers (so far) don't like subscription arrangements when it comes to software.
So the only way to get cash flow is by selling upgrades which (hopefully) offer additional capabilities and value.
I personally think these folks did the right thing, put their cards on the table, and changed their model before it reached crisis level. Hopefully it will work out for them. Lets wish then well. They make a fine product.