I'd see if i could negotiate more, just say 'I've been thinking and i can't sell for less than $1000' and see what they say.
It's like Deal or No Deal, do you take some money now or carry on (hold onto your domain) hope you get another offer further down the line, but same time you might not get another offer of $500, so it's up to you mate.
See with future tech no body knows, i might be wrong but me personally I'd never register a 'holo' domain, because i feel the term won't last, holo (holograms) was just used for promotional purposes, AR/MR aren't really holograms.