> ... understanding is that the workers are limited to 128MB of ram and that they may be 'restarted' at any time. Datasets for accurate browser detection would be really tight in fitting into that amount of RA

I think you might be overestimating that. Bundling the aforementioned https://github.com/faisalman/ua-parser-js wouldn't be significant - maybe hundreds of KB as a script (distinct from memory!) - at most.