Export to other file formats than .vcf, e.g. XML

Is your feature request related to a problem? Please describe.
Currently, the only supported file format for exporting contacts is .vcf - that works good for smart phones, tablets and so on, but isn't supported by many "other" hardware devices, e.g. FRITZ!box DSL router (expects XML), Grandstream SIP phone (expects XML) or other software that doesn't natively use .vcf (Thunderbird, Windows Mail, ...) ... that do support address books, but only in specific formats. Most hardware devices at least support an automated pull.

Describe the solution you'd like
I understand that this is an enhanced feature as even the same formats can be totally different.

The best would be a kind of customizable blueprints (maybe jtemplates?) how the data will be exported. Great would be if some commonly used formats are already supported.

Limitation: will of course not work with pure binary or even encrypted formats.

Describe alternatives you've considered
Either converting manually or writing an own script which both sucks.

The issue names no files, tests, or entry points; begin by locating the current .vcf export implementation and its tests. Define the supported formats or template mechanism from there, with completion requiring a documented way to export contacts in at least the agreed formats and coverage for the resulting output.