Anton,
A field just identifying the recipe as a BrewTroller recipe would be useful. If the user tries to import a non-BT compatible recipe, there may be some additional choices that the user needs to make to help the import process. This can be encoded in the recipe description, but again that seems like a kludge.
The two specific BrewTroller (BT) recipe items for which I found no BeerXml equivalents are Mash Ratio and HLT SetPoint. The BrewTroller has the ability to measure volumes in the HLT and Mash Tun. Given the desired BatchSize it will calculate the required HLT and Mash volume based on several factors, one of which is Mash Ratio. I am not sure exactly how the HLT SetPoint is used - it may be specific to one of the various hardware setups they support.
The BT recipe provides information on up to 6 Mash steps - Mash In, Acid Rest, Protein Rest, Sacch1 Rest, Sacch2 Rest, and Mash Out. It also specifies a Pitch Temperature, which I maped to the temperature of the primary fermentation stage. Other than this field, the BrewTroller does not support the fermentation process. They have a separate product called the FermTroller – same hardware different software. As I am writing this however, I think it may make more sense to map Pitch Temperature to an additional mash step beyond Mash Out.
I am not a brewer, so my understanding of some of these brewing terms is limited.
Tom