While the E-3/4 was the mainstay of bf109s in the Battle of Britain, there were still a very large number of Bf109E-1s in service. The photographic evidence shows the 7mm wing guns were common enough.
As for adding a E-3? There is no need. E-1s and E-3s were essentially the same as E-4s, because they were brought up to the same specs in the field. The only real difference being the canopy.
I don't think HTC can add swappable canopies. It's been asked for on the P-51B for ages. It's not just an exterior graphic swap out, because the cockpit internal files would need changing too, and then all the code to differentiate the selection of which cockpit.
I don't think it's feasible, otherwise we'd have had our malcolm hood P-51B optional on the birdcage airframe.
I, personally, would like to see the E-7 and F-2. The E-7 adds post-BOB options to the Emil line and small improvements, while the F-2 bridges the gap between the spit variants and plays a rather big (tho brief) role in the historic timeline.