*Bug* well more game play bug.
Advanced Shielding, it will obsolete Anti Missile batteries, arcology, and shielding.
Thus once you research this tech, all those previous buildings are no longer available, and as such will leave you cities vulnerable to attack.
The National shield is a world wonder, and only available once. Later players, will have to build an advanced shield.
I believe, it should run the same as the work shop - Factory - industrial complex upgrades line to quote one.
You need A before B to get C allowing D, which gives E.
It shouldn't immediately invalidate the current builds, thus leaving your cities open to attack.
*Edit* As well, while building the National shield, you can't build advanced shielding else where as well, I know that would be self defeating, but if your in a race for the Advance shield, and lose, your immediately set back 10+ turns in you BEST hammer cities, and more in lessor ones. Plus the health benefits and others associated with Arcology, shielding etc
Just my thoughts
I just tested it out myself (after upgrading to v648), and it doesn't completely work the way you are describing it. Replacement buildings don't invalidate the previous buildings until they are completed. Example: Arcology Shielding continues to work in a city with Advanced Shielding available on the build list. In fact, you have to have Arcology before you can build Arcology Shielding, so the Arcology Shielding won't show up until you get the Arcology built. (I tried it in WorldBuilder. Start a new game, found your first city, WB in Factory and Industrial Park on the first city and Megastructure Engineering and Shielding techs. You should see Arcology as buildable but not Arcology Shielding. If you build Arcology and Arcology Shielding, you can add Advanced Shielding tech through WB and Arcology Shielding will still be active.)
The National Shield, on the other hand, is a problem. As long as the National Shield hasn't been built, it will block all your other cities from building any of the Arcology buildings. I think the Hide Replaced Buildings check needs to check if the replacing building is possible to build.