The big advantages of cafes and pubs is that people can come and go, can order food and drink if they wish, and don't look odd if the numbers are small or large. Of course those of us who are driving don't drink alcohol at the pub meets, and I have never found this a problem.
We have occasionally built in other activities (blue plaque hunting in Cambridge and monuments in London if I remember correctly). The only cafe I know in Oxford is Greens which is next to the Bird and Baby in St Giles, is nice, if pricey, but has accessibility issues.
I have often thought an outside meet-up in the summer would be a good idea, with an indoor option for the evening or in the event of rain.
Possibly university, community, religious or GLAM space might be used especially if an additional event was involved, but we would be very lucky to get such a venue on a recurring basis.