I would like to know as well - I would like to have 2 xfinity lines on my iphone xr
1.) It is unlikely that Xfinity Mobile will have eSIM support anytime soon, if ever. The FCC has balked at requiring the major carriers or anyone else to provide it and the major carriers have not made it easy to get it.
2.) Also, iPhones can only have one CDMA carrier, so you would never be able to have two Xfinity Mobile or Verizon lines on one phone.
You can have an Xfinity Mobile SIM and an AT&T or T-Mobile eSIM but it takes a little work.