Funny enough, I was asked about trying to mirror something similar just the other day.
With respect to the 'Talk to me about' field, you are correct that it's a giant open-text field you could put data like that in. I would caution that it's also user-editable, and it may not be obviously intuitive to them that the data loaded there is meant to be used differently. The other caution is that building later reporting on it may be very difficult versus something like a multi-select drop-down menu that controls the options people can pick and standardizes spelling on them.
If/when I move forward with my variant, I'll add field(s) to a Custom Form that's attached to every user in my instance. It holds things like their unique IDs in other platforms for integration purposes but also custom attributes like this discussion. If I've got a small enough list of tag-able skills, it would likely just be one form element. If I really needed to create families of skillsets, I might make multiples, but again think about future reporting needs first.
