I've only been in two micro-pubs, neither are 'middle class in nature', the first that opened in town, the 'Anchored in Worthing', mainly a real ale fan base, with people from all backgrounds, they moved recently and I've not get been in the new place, but in the old place they didn't serve coffee. Based on the description below, they also didn't sell 'craft beer', just local real ales straight from the cask, plus Sussex ciders and wines.
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Then this one I discovered hidden in the back of the village farm shop & deli, which has become my local.
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Now, being in the back of a farm shop & deli, and in this village, I expected it may be more middle class, but it isn't, it's a proper local pub, with a mix of customers, including retail & council workers, a gardener, a train driver, a luggage handler that works at Gatwick, etc.
Again no 'craft beer', but Sussex ales, ciders, lagers, wines, and and a range of spirits, where possible locally produced. They do serve tea and coffee at anytime, and a limited menu from noon to 4pm, plus Friday is pizza night, and weather permitting a BBQ out the front on Sundays, all much like any normal pub.
I am sure some micro-pubs are probably more middle class, depending on the area, but that happens with normal pubs too.