I've read the article, watched the report on BBC News and visited the website. Each to their own, but I'm not enthusiastic enough to get involved.
Regarding path maintenance: As I write, I'm in dispute with Kent County Council at Ombudsman level because of their failure to fulfil their obligations - I'm quite proactive in that regard. Should a system of 'Slow Paths' come into being, then I assume these would be given a higher-than-average priority - perhaps similar to that of 'Promoted Paths' - in the triage system that prioritises path maintenance. This could have the effect of allowing lower priority rights-of-way to become even more neglected in an already overworked and underfunded system.
The perceived need for Slow Maps (seems to me) to be based largely on the total uselessness of Google's provision for walking routes. I've just asked Google to show me the best walking route between Whitstable and Faversham, about 10 miles away. Google completely ignored the blindingly obvious (to anyone who glances at an OS map) 'diamond' Saxon Shore Way route along the coast between the two towns, instead recommending a dangerous inland route along roads with blind bends and no footpath.
While many towns and other urban areas can be easily linked by 'recommended' walking routes, others cannot. For example, walking the 7 miles or so safely between Herne Bay and Canterbury on existing PRoWs and avoiding busy roads requires a much lengthier and very convoluted route. This could be done of course, but waymarking the route would involve a significant cost.
Finally (and perhaps selfishly!), I'm not interested in getting other people out walking - I'll leave that to them. I walk solo or with my immediate family. I've noticed a significant increase in the number of walkers, runners and cyclists in recent times, many of whom require me to take avoiding action if I'm to stay a sensible distance from them, because they don't seem too bothered. I'd be happy to return to the good old days when I'd hardly see another soul when I'm out and about...