Amit,
We seem to be seeing an increasing number of such requests, and lots of discussion on parser and markdown standards, also about integrations
I am also keen to build setting json files and windows command files within tiddlywiki.
One advantage in tiddlywiki is information can be stored and referenced in many ways to help populate the content, you may reuse elsewhere.
In Every case the key issue is what are the formats and standards that tiddlywiki needs to implement to achieve this.
Sure putting a call out for a particular format such as your suggested "anki flash cards (.apkg)" may result in some one with prior work who can point you in the right direction. But this is less likely with more obscure apps. For example there exists solutions already for Microsoft Excel.
However more likely the questions becomes can we create this? To know if it is possible a basic outline of the format and standards within a anki flash cards (.apkg) file will be necessary.
An Example may be if it used an XML or json format, and also if the application actually accepted other import formats, as suggested by Mark.
It may be a simple matter of not using the native file format but but exporting in a format shared by both the app and tiddlywiki.
Have a look around you app, and search this forum for any alternate formats that may be common. Then you may be able to ask more specific questions.
Regards
Tony