News Microsoft 365 subscription service unveiled at Inspire

At £15.50 a month (£186 a year), compared to a copy of Windows 10 pro (£220) plus Office H&SB (£230), you break even after 29 months, or two and a half years. That's roughly in line with the Office update schedule, but with Windows 10 going to a rolling version update by default even for retail copies, whether a subscription makes sense depends on what extra support you gain, and whether you have a lot of churn in deployments (managing porting license keys is a chore and can easily end up wasting money on 'lost' keys or licenses that do not operate for their whole lifetime).
At the very least it removes the excuse of "but we already brought a copy, we need to use it till it breaks!" for not keeping systems updated, which is a net positive for everyone.