She's probably had enough of us - or at least me - but a version with Polish markings at Cassino would be great. A desert version would probably be the most popular. Also, did the Russians get any of these? If so, that would be interesting.
The Russians got exclusively M4A2 models as they only wanted diesel engines in tanks. They got several sub-versions, i.e. M4A2 75mm "dry stowage", M4A2 75mm with late hull and M4A2 76mm. Unfortunately the M4A1 76mm like HB seems to be planning is not applicable to the Russians. They were primarily used by the US Army in Europe, the British in Europe and Italy, a few by the Polish armored division and a few to the French later on. The M4A1 with 76mm gun came into use with the US Army in mid-July, 1944 in Normandy with the US 2nd and 3rd Armored Divisions. Later deliveries added other units to the list and some deliveries went to the British (who supplied the Polish tanks).
A "desert version" would be an early M4A1 or M4A2 and could be done as a US tank from Tunisia ,also.
HB MIGHT want to consider the M4A2 with 75mm gun and the earlier hull as a possible future production type as these offer a number of paint possibilities. The M4A2 was not favored by the US Army for overseas service, but was used in the US for training (OD with full stars and the white turret stripe), they were supplied to the USSR (delivered in US OD, but the Russians added their markings, and some probably got winter whitewash), to the British (painted for Sicily, Normandy, etc), to the Free French (with marking variations between the Free French 2nd Armored Division that served with Patton in Normandy and the Free French 1st Army that came up from the Mediterranean), and to the USMC in the Pacific (delivered in US Army OD, but some were later camoflage painted). That is quite a few paint jobs and minor detail variations for one basic tank model!
As far as "Polish Shermans" at Cassino - I wasn't aware that the Poles had any of their own tanks at Cassino. I think they had tank support from the British or US Army.
As far as a DD tank, I would love to see one, too. HOWEVER to do one right involves a very complex model. The screens are tricky to model in any scale (I did a US version in 1/72nd scale once) and there is a LOT of bracings and fittings with the screens up or down. The propellers and their drives aren't too hard, but those screens would be a pain to cast correctly - making a DD tank an expensive proposition.
Gary