In a way, yes - there are Oharty's scripts for Piratez I haven't seen them yet, but they should be pretty straightforward.
A bigger issue would be a designing one. Right now, we have two shields - standard and plastasteel alien alloy - both applicable to the relevant armour. But if the shield becomes a separate entity, not bound to a particular armour, what should it be like? Do we still keep the two designs, unlocked at the same time as the armours? If not, which one should be kept, and when should it become available? Do we need more shield types?
Keep the same parameters and prerequisites as now
Alloy shield does not reduce TU and is manufactured, the other shield comes with Xenonauts' armored vest and becomes purchaseable much earlier. Why not have both?
In-universe, it makes sense that X-COM should try to gain access to something like police riot shields. That's the one that comes with Xenonauts' armored vest. Personally, I'd prefer to have it as early as possible
Maybe this set of armour should appear after researching Kiryu-Kai and Xenonauts should give something else. After all, Kiryu-Kai was about applying brute force to the problem.
Alternatively, this shield may come with kevlar vests.
Also it would make sense in-universe that X-COM would try to recreate the armour, shield included, when they learn to process alien alloys.
Since there's a symmetry between the original UFO and TFTD, there can be a shield from aqua plastics. Or an explanation why that won't work
