I don't know if this really amounts to a *strong* objection. To me, as much as I try to like it reading this thread, the colon just continues to feel wrong to me. Yes, of course I know the analogy with lambda, and I can even see a certain analogy with dict literals. However, far more compelling to me is making it look more like the ternary expression (which it is really basically a special case of.
In terms of keywords to put in place of the colon, the "least bad" in my mind is "return." Yes, of course, we don't actually return out of a function call or remove a call stack element (well, unless we wind up doing so in the implementation). But without fuzzing one's brain *too much* one can think of the except expression as kind of like a function call, and though of that way, 'return' makes sense.
The next "least bad" in my mind is 'else' because if preserved the parallel with 'val if cond else fallback' most closely. Sure, we need a bit more verbosity in the expression, especially when 'as' is used (and it should be included), i.e.:
x = val except SomeError as e else something(e)
But still it's basically only substituting the one 'if' for an 'except' and otherwise keeping the familiar ternary expression.
Of course, my opinion here is of very slight value, since the intuitions of our BDFL will decide the outcome, and the various alternatives are present in the PEP. And indeed, if the colon is what "wins", I'll learn to use it and be more comfortable with it.