Pretty sad that a "defender of the Second Amendment" would propose something like this.
Reading what he said, I don't think it's properly speaking supposed to be a prohibition on adding ANY new parts to ANY gun.
Sen. McLachlan noted that assault weapons manufactured prior to the state's 1993 ban may be dismantled to recycle the part containing the gun’s serial number and rebuilt with modern parts that would otherwise fall under the existing assault weapons ban.
"I plan to submit a bill that seeks to correct this
deficiency," Sen. McLachlan said. . .
I think the "loophole" is CT statute 53-202m:
http://www.cga.ct.gov/current/pub/chap943.htm#Sec53-202m.htm
Sec. 53-202m. Circumstances when assault weapons exempt from limitations on transfers and registration requirements. Notwithstanding any provision of the general statutes, sections 53-202a to 53-202l, inclusive, shall not be construed to limit the transfer or require the registration of an assault weapon as defined in subdivision (3) or (4) of subsection (a) of section 53-202a, provided such firearm was legally manufactured prior to September 13, 1994.
For reference, 53-202a is the definition of an "assault weapon", and 53-202m covers pretty much all the law about "assault weapons". Including the requirement to register it. So 53-202m is the "pre-ban" loophole--if you have a stripped lower legally manufactured before Sept. 13, 1994, it cannot by definition be an "assault weapon" no matter how many "evil features" you put on it. Practically speaking, this means that anything manufactured before the ban date is just another firearm, as long as it's not select-fire and/or automatic-fire capable. It is totally exempt from "assault weapons" law.
Folks I've spoken to always seem to think of it as a "gray area", just like a few years ago we thought OC was legally gray until folks actually tested it and prevailed in court. It's likely that if police discovered your AR-15 with a bayonet lug and pistol grip, they wouldn't care that the serialized stripped lower was manufactured before Sept. 13, 1994, but would consider it an assault weapon anyway. No one I've spoken to wants to test it.
However, it seems that our frenemy Sen. Michael McLachlan wants to close that "loophole". I'm betting he'd require registration of ANY gun which meets "assault-rifle" criteria, and they'd use the "type" language to require registration of AR-15s. The law talks about the "Avtomat Kalashnikov AK-47 type" as a named "assault weapon", and from what I understand that's practically meant that anything that functions like an AK-47 and fires the 7.62x39mm round is banned no matter what name (or lack thereof) is stamped on the reciever. So banning the "AR-15 type" would mean that any AR-15 would be banned--though it might be possible to circumvent it by chambering your AR in something other than .223 (or perhaps other than 5.56x45mm).
Does this make any sense? Scratch that. In the nonsensical context of banning weapons by cosmetic features, does this add up?