The current situation is that we do keep GSA alive even on svelte devices, even when using Custom Tabs, and the histogram from the field is here:

https://uma.googleplex.com/p/chrome/histograms/?endDate=20170214&dayCount=1&histograms=Search.GsaProcessMemoryPss&fixupData=true&showMax=true&filters=channel%2Ceq%2C4%2Cplatform%2Ceq%2CA%2Chw_ram%2Cle%2C512%2Cisofficial%2Ceq%2CTrue&implicitFilters=isofficial

Looks like a 20-30MB saving!