I don't think Johnson is in with much of a chance. While he's undoubtedly very popular with the Conservative Associations, who decide between the last two candidates left in the race after Conservative MPs have voted in the preliminary rounds, I don't think his colleagues in the Parliamentary Conservative Party regard him very highly, either as a colleague or a potential leader.
Nor do I think that, right now, the Conservatives are looking for a long-term leader. They want someone to take over, navigate us through this horrible mess TM has put us into, if that's at all possible, and then to stand down while they choose a more permanent leader who can, they hope, lead them into a successful general election.
The serious leadership candidates -- Dominic Raab, Sajid Javid, Jeremy Hunt and the like -- are keeping very quiet at the moment (as, indeed, are Boris Johnson and Michael Gove). They don't want the job right now.
They want someone else to get us out of the mess, upsetting a lot of Conservatives in the process (which is going to happen, whatever the outcome) and then to step down, suitably rewarded, and let someone new take over with a clean slate.
That person, whoever it is, will then be able to say that, while they share colleagues' discontent with some aspects of whatever solution their predecessor was able to implement, that's now past history, and they want to get on with making it (whatever "it" turns out to be) work.