The final part of the EM7455 Linux driver support is going in Linux v4.7 which will be released in a couple of weeks. It will also be backported to the currently maintained stable kernels, so you should eventually get it through Ubuntu kernel updates.
Sorry it took this long. In theory, any MBIM modem should just work with the existing Linux drivers. But it turned out that the EM7455 needed a small delay during initialization, or it would silently fail to work. The "fix" is a single line of code:
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