Objection your honor: assumes facts not in evidence: head-house enclosures were mostly deleted and will not be built from scratch or any other material
Every single GLX station has at least one "STATION HEADHOUSE"
per design documents. Headhouses may not have glass windows and climate control, and some may not have roofs, but I believe all stations but one will be "enclosed" in that access points are walled and secure-able "enclosures." These stations are much more like Lansdowne or Boston Landing than, say, Coolidge Corner.
Lechmere will have two grade-separated headhouses with walls and ceilings.
Union will have an walled entry way with a close-able security gate.
East Somerville has a single at-grade primary access points and an additional emergency egress.
Gilman Square will have walled and roofed entry corridors.
Magoun Square will have a walled and roofed entry corridor.
Ball Square will have walled and roofed entry corridors with security gates.
Medford / Tufts will have a walled and roofed entry corridor.
These are not strips of concrete like on the western reaches of the GL, they are grade separated structures with walls and controlled access. Some of them have such clear controlled entry points that you almost have to go out of your way
not to faregate them.
I'm anti-GLX faregates, and frankly removing them at Science Park and Symphony also makes sense. They make adding addition entrances and egresses more difficult (this actually matters a lot at Symphony due to ADA requirements possibly mandating two elevator locations). They increase operating and capital costs and should not be significantly faster than Type-10 boarding, with two tap readers per door
But these are brand new mostly grade-separated entrances and exits that are already ADA compliant with brand new elevators and brand new staircases. We're not going to be adding entrances or egresses to these stations in the next half-century. Also, the GLX will be fully operational for years (decades?) before the entire fleet is replaced with Type-10s.