I was thinking along those same lines, but parallel mechs are a niche inside a niche so if it could be switched between parallel mode and series mode, that would probably attract more buyers. The only parallel mech that I currently own is the Strombreaker mod by Vaperz Cloud, but it is a triple 21700 battery mod so even though the weight of the mod itself (i.e., without the added weight of the batteries) is not heavy by any means, and even though it is ergonomically shaped (similar to how the Rage squonker is ergonomically shaped also), a lot of people are going to say it really is clunky still nevertheless. But to make it switchable between parallel mode and series mode, in order to make it safe with regards to the user of the mod remembering to insert the batteries correctly (using the correct battery orientation), I'd say the battery contacts would need to be designed following a principle that is similar to the contact on the battery door of the Hammer Of God V3.2 as that one serves the purpose of a fuse that melts if a battery is inserted wrong. (My Hammer Of God "Hellhound" also came with a spare contact that was inside a separate bag, not tossed into the same bag that had all the other spare parts in it, and, both bags were stored inside the mod to save on packaging material and space.)
That said, I also like the form factor of the Noisy Cricket II-25 by Wismec, as that one makes a 25mm atomizer sit flush on it despite it really is both small and ergonomically shaped as far as the shape and dimensions of the body of the mod are concerned, but it isn't a mech mod, and, there are a few things I don't like about the safety design of the Noisy Cricket V1 even though the revision of it that has the knurled button is not a bad mech mod, it actually hits hard, and it's dirt cheap so it does prove that a mech mod doesn't have to be super expensive to perform well, but the V1 will only make a 22mm atomizer sit flush, and, in terms of the safety it would have been loads better if I could eject the batteries at the simple flick of a spring loaded latch on the bottom just like the Hammer Of God V3.2 and the Stormbreaker. Another example of a regulated mod that could have been a palpable mech mod IMO in terms of the look and feel of the mod is the Double Barrel V3 by Squid Industries. If they'd make it a parallel-convertible-to-series mech with the side firing mechanism of the Side Piece by Purge Mods, then I'd probably be yelling "Shut Up And Take My Money".