This will likely be rejected for one the same reasons that they decided they would not add any new flag emojis. Flags come and go. Bitcoin hasn't even been around for 20 years yet, and its future is highly uncertain.
Also, considered as a currency, it would be better as a regular text character, not an emoji. Like $, €, ¥, £, etc.
I guarantee you, T-Mobile does not hesitate to hand over any and all data they have to the government. And they don't encrypt shit, as evidenced by their many many data breaches.
The postal service is from a different era, and has legal protections I wish online equivalents had. Logically they should. Realistically they probably never will.