Did a 'stress test' of the beta software.
With all the data that is scanned as text, and the reference thumbnail, 3327 photos resulted in a database size of 206.4 Mb on a Mac.
Which is about 0.062 Mb per photo, which is about 6200 Mb for 100,000 photos (just over 6 Gb).
Not bad. My one million photos I have to scan could be just over a 60Gb database. Good to know!