There are some big players already present on the market such as Tangem (only contactless) or Satochip (dual-interface).
Arculus, Cryptnox and CoolWallet are also worth to mention.
Do you plan to open your "shell" to other smartcard player for a better interroperability?
I have Tangem 2 and use it primarily to top up my crypto card while on the go. Because of that, I would have little interest in their "shell" accessory
which requires the wired connection. One of the key advantages of Tangem is that it connects wirelessly via NFC to its dedicated mobile app
which is very convenient for mobile use.