Yesterday Riot announced upcoming in patch 11.17 system requirements incerese. They're changing minimal shader device to graphic card with 1 gb vram. Also recommended section suggests 4x more vram, from 512 mb to 2gb.
It comes up nicely with next event, because patch 11.16 is 3 weeks on PBE.
Reav3 in His April Devblog said " [...] we’ve decided our gloomy new yordle needed a bit more time in development as we needed to create some new tech to visually sell her source of power. " It can be new shadow mechanic, because Vex companion is actually a shadow.
Also, in visual novel, Vex summoned large shadow beneath sentinels to slow thier movement, this could be new mechanic or very heavy shadow mechanic rework.