"Sensible policy would be to press for the transitional arrangement to last as long as necesary so that all the issues can be worked out."
You are making a couple of assumptions here, unfortunately.
It is not clear that the issues can be 'worked out' given that a minority support any specific end goal. The plurality seems to favour a soft Brexit considered individually, but no Brexit as a second choice seems to have a majority... but you would have to have some kind of first choice/second choice mechanism, which the Brexitines would fight tooth and nail.
It is also unlikely that the EU would accept, potentially, decades of uncertainty and distraction, while allowing undue access to their market for a nonmember to go on indefinitely.
It is surprising how often opinions show up in the British press that seem to assume unilateral British control over the processes and events.... along with other delusions that will bite the UK in the ass in coming months and years.