I'm in two minds about it.
Asking for an extension of paid maternity leave, owing to the current circumstances, isn't a particularly outlandish idea. There will be a huge difference between my first maternity leave a year ago, and mine starting in 4 weeks. My newborn won't get to meet family for months at this rate, nor will she get to go out more than once a day in her pram, get to go to baby-friendly activities, etc. While I'm sure she'll be fine (I am lucky to have a garden and plenty of baby toys in my home so I can make up the short fall in her being out and about less), I'm not so sure I will be.
My mental health took an absolute battering last time (TLDR: traumatic birth experience contributed to PND for 6 months post partum). And that was with me being able to get out and about, see family and friends, etc. I think a lot of mums, especially FTM's, will struggle with their MH this time round because when their partners go back to work, they won't be able to access other forms of support/coping mechanisms. Therefore, extending maternity leave at least gives these mums more time to recover and have a few enjoyable months off if they do develop PND/PPS.
However, I think proposing the extension of maternity leave purely because baby groups are cancelled actually takes away genuine valid concerns a lot of mums may have, and dumbs the whole thing down. It makes it laughable. Instead of explaining to people the consequences of lockdown on vulnerable and struggling mums, it makes the whole thing look like a bunch of mums are mad because they don't get free coffee every Tuesday.