Lofstrom Loop tech, but at a smaller scale?

I'm sure that all or most of us are familiar with
Lofstrom loops, orbital ring systems, mass stream
technology, that sort of thing. Just in case, here
are some links.

http://en.wikipedia.org/wiki/Lofstrom_loop
http://en.wikipedia.org/wiki/Orbital_ring
http://en.wikipedia.org/wiki/Space_fountain

When I read about this stuff, they start out talking
about orbital rings, Lofstrom loops, space fountains,
and so on. Then, the author will jump to a smaller
scale and talk about suspension bridges a hundred Km
long or buildings ten Km tall. Then it's on to
supramundane worlds and Dyson spheres. OK, I kid a
little, and it's really quite fascinating.
http://www.orionsarm.com/eg-article/4847416b8b0ad

I'd like to consider a smaller scale than even the
ten Km high building. Like maybe a sphere one hundred
metres, even fifty metres across. Make it airtight,
have one atm inside, and sink it to the bottom of the
ocean. Use the mass streams to hold it against the
pressure of the water. Maybe use this to hold a
surface colony against the pressure of the atmosphere
of Venus.

And now for a crazy little idea I've been holding in
abeyance:
Any reason you couldn't build a vacuum airship this way?