This seems like a fairly sensible strategy due to the hand-face contact it inevitably causes. It seems a few TOCs have already started doing this
https://www.rssb.co.uk/en/Insights-and-News/Coronavirus-pandemic-how-we-can-help-you
https://www.rssb.co.uk/en/Insights-and-News/Coronavirus-pandemic-how-we-can-help-you
Advice on the use of whistles during the COVID-19 pandemic
We are advising that the use of whistles on platforms and stations (for example, as part of the train dispatch process), should cease for the duration of the COVID-19 pandemic to remove an infection risk to employees where safer alternatives can be used. Our advice is on a one-pager which you can download.