Proposal to add 'Bengali Letter Khanda Ta' to the Bengali Block (initial version)

Introduction
Two methods have been two proposed to enable Bengali Khanda Ta to be encoded in Unicode text, and these are outlined below.

As I hope you will see, they are both unsatisfactory, and so the Bengali letter Khanda Ta needs to be allocated a separate Unicode point.

Method 1
It has been suggested that Bengali Khanda Ta should be treated as a half form of Ta, and can be explicitly encoded as Ta+Virama+ZWJ. However, this is unsatisfactory as it precludes the ability to encode half forms of Ta. Such forms are commonly used in some font designs. Examples are the ISFOC fonts as used in CDAC ISCII based applications (example shown below).

Typing with ISFOC Fonts in iLEAP. (INV is the ISCII equivalent to ZWJ.)

Method 2
Another proposal put forward is that rendering systems should display the sequence 'Ta+Virama' as 'Khanda Ta' as the norm, and an input sequence such as a Ta+Virama+Consonant should be displayed as either 'Khanda Ta + Consonant' or a 'Ta+Consonant conjunct' as appropriate.

However, this proposal does not work either. The correct display of a Ta+Virama+Consonant sequence is very context dependent as shown below.

Differing ways to represent the Ta+Virama+Ma combination

This example shows that in order to display the correct spelling of the word 'satmaa', the Ta_Ma needs to be displayed as Khanda Ta+Ma, and in order to display the correct form of the word 'sadaatmaa' it needs to be displayed as a Ta_Ma_conjunct.

As the use of ZWJ to control the above sequences has already been precluded by 'method 1', we are now left only with the possibility of using a ZWNJ to control the display of the sequence. However the Unicode standard has allocated the ZWNJ to the specific purpose of producing explicit Virama forms. Hence, the only solution is to allocate the Bengali Letter Khanda Ta to a specific code point in the Bengali Block.