It's still worth noting when optimization is practical or not, Squirrelloid.
As far as DMs allowing it, I'd expect it to depend on the mindset of the DM(and I don't just mean those who go for RAW over RAI).
If a DM REALLY examines the implications of this loophole, he might realize it's not so bad: Paragon Multiclassing sucks. There are 2 rules possibilities I've seen so far that make it suck
less. This is one, and the other is the possibility of using the replacement class feature to gain higher-level powers from your paragon multiclass. Both are rules that the careful DM will likely houserule, but when he realizes the character is still not unbalanced, but he may let it slide.
So it's entirely possible to have a DM who lets it slide based simply on the fact that it's not a big deal. This makes it more 'practical optimization' than Blade Cascade cheese ever was(despite Blade Cascade having a more firm rules basis).