If your only value metric is about personal storage, then you might see Dropbox as 'doomed' by its more-space-for-less-cost competitors.
I've worked with Dropbox and OneDrive and despite many people having access to a nominal TB of OneDrive storage via Office365 subscriptions, the creaky, Sharepoint underpinnings of the latter still make it a poor alternative to Dropbox for simple collaboration and sync. You can't just drop a bunch of files into the relevant folder on your HD and have them shared and synced; things like file name limitations will crop up, stalling the process indefinitely, and users don't see why it's their responsibility to work around those sort of things.
As far as collaboration is concerned, the ubiquity of Dropbox across platforms will keep it in front for some time to come.
I've worked with Dropbox and OneDrive and despite many people having access to a nominal TB of OneDrive storage via Office365 subscriptions, the creaky, Sharepoint underpinnings of the latter still make it a poor alternative to Dropbox for simple collaboration and sync. You can't just drop a bunch of files into the relevant folder on your HD and have them shared and synced; things like file name limitations will crop up, stalling the process indefinitely, and users don't see why it's their responsibility to work around those sort of things.
As far as collaboration is concerned, the ubiquity of Dropbox across platforms will keep it in front for some time to come.