What if Duskblade's damage had a stacking mechanic when unseen that decays when unseen?

Now, hear me out. I don't want any of the 'just delete duskblade lul' as it provides for a meaningless discussion.

Now here's the idea: Stats and passive remain the same except for:

Unique Passive - Nightstalker [Reworked] : Damage changes from 30-200 after being unseen for 1 second and melees slow by 99% to -> your next attack does 0 damage + 0% slow, gaining an additional 8 - 50 (based on levels) and the slow increases by 19.9% for every second you remain unseen, stacking up to 5 times (max dmg 40-250, ~99% slow). One stack falls off every 1 second you're seen by champion vision (not ward vision, otherwise too much vision control - too op in high elo)

Why this could work: Assassins can't just walk up to your lane go 'lol, let me just blow my full combo and auto for that delicious db proc.' Now they need to actually play like an assassin, flashing over the walls, using their stealth effectively etc. to make sure their stacks don't fall off (and then doing no damage). Rewards biding their time and going for the strike when the time is right instead of going kamikaze.

You can't also use it during laning phase, reducing its rush effectiveness and oppressiveness.

Also allows some small counterplay. Manage to run merry-go-rounds the assassin as he chases you? Congrats, his db does no damage to you (though you may still die due to this high-dmg-meta).

Thoughts?