I've tried to use the train to do work but I find the WiFi not reliable enough or the mobile data connection if I bypass the WiFi.
The laptop I use connects into a Virtual Private Network (VPN). Even just using Google apps, it loses the connection. For data protection reasons I can't have offline working switched on for the Google Apps.
However despite that I prefer office working to home working so I'll still travel in.
I tend to do work that doesn't rely on the wi-fi. E.g. pre-download e-mails, write responses and queue back to send when I've got connection. Or write reports, etc.
The wi-fi I used most (Great Northern, Thameslink, Greater Anglia and Cross Country) I find reliable for exchanging e-mails etc.
I think leisure travel particularly locally will rocket as people want to get back out and about. I'll be interested to see what happens with commuters. Most of my regulars are not work from home types so we shall see but long distance commuting to London may well change.
Leisure travel will no doubt be kick started by some fares offers once normality resumes.