Mark Weston is of course the Councillor for Henbury & Brentry - I suspect that a fair chunk of his constituents work in Avonmouth and would benefit from an extension of the line to Severn Beach / Avonmouth, particularly if a new station was built near the Amazon depot.
Some years ago, I was working in the now closed Jobcentre in Stapleton Road. I wasn't doing work coaching stuff, but was aware of developments. A logistics centre in Severn Beach, before Amazon, needed night shift staff. I realised that very few people seemed to know that Severn Beach was accessible by train. One manager, who in fairness lived elsewhere, asked how people would get to Temple Meads, and was shocked when I pointed out the station a couple of hundred metres away. Despite this, I saw a number of young men without their own transport jump at the chance, showing that rumours of nobody wanting a job were unfounded, none of whom were put off by the train times not fitting the shift pattern. Alas, having to arrive at work almost an hour before the shift starts, then spend over an hour in a shelter on the the platform hoping the first train home wasn't cancelled can knock the enthusiasm out of the keenest young worker. Many did not last the second week. I suggested asking the company to be more flexible with timings, but despite their desperation for staff, they couldn't/wouldn't change. Which is sad.
Mark Weston is probably in a far better position to talk to employers on Severnside and in Avonmouth about things like this, and may be able to boost any business case for the loop with answers to the right questions. Poor transport links are often cited as a hurdle to employment and expansion, so why not take the opportunity to do some real in-depth research into not what would be achieved as things stand, but what could be achieved by linking housing and employment centres well away from the traditional central area.