What if SightStone had a stacking passive?

Like if you placed 15 wards (obviously done in some non-spamable way such as sitting in fountain just placing wards), you can permanently hold 1 additional ward. This applies to only these items . Then, once you get your 5th ward, every 120 seconds you will regenerate 1 ward.

Not really sure how to make this not able to be spammed through but maybe if the wards had to each last at least 1 minute to count towards the 15 total. Multiple wards out at the same time would each count individually. So a fastest time to get the 15 stacks would be just a bit over 5 minutes. Also, trinket wards and control wards do not count towards this total.