First of all, thanks a lot to all who have devoted their precious time and knowledge to develop and release this excellent freeware to the Bangla-speaking people all over the world. Hats off to you, champions!
As far as a typing interface goes, Avro truly leaves very little scope to whine about. Just one feature that I really felt can be suggested at this time is an Alphabet Choice Menu.
Alphabet Choice Menu: Multiple alphabets with similar sounds (such as 'Ta, Tha, Taw, Thaw') can be located under one key ('T' key, here). Here is the concept: When the user hits the 'T' key (that already has 'Ta, Tha, Taw, Thaw' assigned to it), the base alphabet 'Ta' would appear underlined/dotted-underlined, giving the user a hint that there are several other choices available (SHIFT+T would show 'Tha,' but would act in the same manner as well). To select the right alphabet, all they have to do is to press a pre-defined key (maybe CTRL/F1~F12) that will bring up a drop down menu with all the alphabets of the similar sound (in this case, all four choices). Then using the arrow keys, the desired alphabet can be chosen and confirmed by hitting ENTER. Afterwards, when a new alphabet key is pressed, the selection hinting underline would disappear.
This arrangement can substantially reduce the allocation problem between several alphabets (for example, in Avro, 'U' would be able to house 'Hrossho-Uu', 'Dirgho-Uu' and 'Uu-kaar's, leaving 'D' free for 'Da' and 'Dha') and can also be used to display JUKTAKKHORs. The selection method from the menu can be further simplified by assigning simple shortcuts, but its upto the developer to device the way. Anyway, an Alphabet Choice Menu might make the Avro interface even more phonetic and would definitely leave a couple of keys free on the keyboard to house some other alphabet.
Thanks!