Actually Five Guys have already opened up outlets outside of the South East of England. They'll also be opening up outlets in Bristol and Glasgow, more or less simultaneously, with the Cardiff branch. Looks a bit overrated imo.
Burger and lobster is the real coup, upmarket with very few outlets and a unique concept (for Cardiff anyway).
They're the sort of businesses that would have passed us over not so long ago. Suggests there's now a market for slightly higher market chains.
I will say though that, there's a bit of a deficiency as far as a presence of local, home grown chains (big or small), or independent equivalents are concerned. It'd be nice to see that develop more. In fact it would very beneficial for Cardiff to produce more local chains, especially if they were to expand into other towns and cities elsewhere in The UK, assuming they would have their headquarters in Wales. Bristol has been very successful at this, with a long legacy of managing to grow and accommodate both local and non local, chain and independent businesses alike; The loungers group, Boston Tea Party, Las Iguanas (plus Turtle Bay), ZaZa Bazaar, Grillstock etc all began in the city and have all expanded into other parts of the country to varying degrees.
Cardiff does have a few decent contenders; Barker Coffee could be Cardiff's (and Wales') version of Boston Tea Party, and La Bodega could also definitely go places, to name just two local places.