If you want to design a cap - Goog probably has an idea of the kinds of file people store (whether it's pics or docs or videos or sheets etc...), pick a number of those that's impressive and is just lower than what your 10% power users has, and then use that to influence the package size.
2TB of files can easily be turned into "half a million photos" or like their previous ad campaigns, show how it can store every photo from birth to university for your kid or something. Or a love letter every day from first date to goodbye.
If you can't compete on the number, don't compete on the number.
This is why I so strongly prefer services that don't bullshit me. Tell me what you're exactly selling, for how much. If promise to livestream setting your marketing department on fire, I'll pay double.
 If it is free, I already know what it costs and am not interested, thanks.