Yet another idea thrown out for fun.
Have some spells that their lag isn't after the spell, but before it comes into affect. Where I see thats how spells are in general, that is, casting time, then spell affect...if the system is built as it is now, I think there still could be some fun with this.
Just as an example, think about Meteor Swarm...have the spell cast, but have the lag upfront, like...
Name begins to concentrate, chanting the words 'Blah Blah Blah'
A small meteor arcs towards you in the sky.
lapse 1 round where the caster is lagged
Spell hits, lag is over for caster in same round.
Would add some fun to spell casting, putting some more strategy with timing and see how fast people can flee when they see some nasty stuff coming their way, hah.
Yeah, another idea, open fire.
Plague and poison? I suppose minister to some affect. Clerics or shamans have something like this. Spells like this exist.
WC
Sadly it would be a bit unbalancing, one could be ready for the cast, flee, spell goes off, return unhit by the spell and beat on the mage while they are lagged.
or stack spells that were different...
c lags before
c lags after
they hit in the same round, talk about a killer.
Ugh, not really, those are still cast in the same fashion as all other spells. You cast, fail or succeed, then are lagged for a predefined time. Mal's are not exactly the same as what I am talking about.
Maybe its a small difference, but if you note how the lag occurs...
it would go Cast->lag->spell Effect, not the standard Cast->Spell Effect->Lag
The swarm is an example of something fun you could do with it, as in having the precursor to the spell and then the hit.
Problem with your way is that spells that fail have minimal if any lag. Your way, all spells would lag regardless of outcome, success or failure.
mutters Fail casting blood vow or malform and tell me spells that fail have minimal lag. 
That's just my special "welcome back" package I set up for you.
And only you. 
Ah, but I haven't rolled up a DK since I got back, so... hah! 
mutters Fail casting blood vow or malform and tell me spells that fail have minimal lag. 
Blood vow lags you like that even if you fail?! NOOOOO!
I'm both patient and well-prepared. 
Just for that, I refuse to roll up another DK. 