as it's obviously in the Commonwealth Map, where may we find it? will it be off the Map like The Glowing Sea is?

Perhaps the area above Natick bank and all that. There is a road leading up to some old warehouses and a kind of transformer station or something (A Behemoth and several Deathclaws usually roams up there) could be a candidate.

Also, the upper left and lower right of the glowing sea are big empty places ( http://imgur.com/SxKOjio) good candidates as well.

It could be put underground, in which case, it could be many places, including under a place like University Point. Well, remains to be seen

It could be in the glowing sea since robots don't have to worry about radiation.

Not much to go on, but I suppose it could be under one of the Red Rockets...

If the gent has walked up to the Commonwealth from D.C. since FO3, he'd arrive in the southeast. Would kinda' add to the fun if his 'bots were built in the Glowing Sea and were crazy radioactive.

The http://fallout.wikia.com/wiki/Electrical_Hobbyist seemed really strange to me but sort of fits the bill. Bethesda would probably just add the underground section we saw in the video.

Nah, all hidden bases in the Commonwealth are under donut shops.

Huh. Never found that place. That would be a pretty set place.

Plus it wouldn't be the first time a previous location was used in a DLC.