The problem is without door-to-door , the whole basis of the religion kind of fizzles away. Half or more of the meeting content is directly or indirectly about doing "the ministry". Ostensibly , it is all about preaching the good news as Armageddon is near. I just can't see that ever being replaced with letter writing or whatever.
Franz relates in his books that when the GB discussed the ( extremely shaky ) scriptural basis of D to D , one of the GB members said ( I'm paraphrasing here ) "if we don't have door-to-door , what will the brothers do? They will do nothing. "
And I would take with a big pinch of salt the "150 contacts a day" on the website. For a start , for a country of 328 million , this represents 0.0016% of the population. Also note how he said was careful to say that this was people who "reach out in some way." A lot will be bogus / timewasters - very few will be actually people requesting bible studies or even having any interest.
I say this as someone who was the service overseer for many years and used to follow up on people who filled in "contact us" slips that were often printed in Kingdom News tracts , Watchtowers etc and forwarded to us by Bethel. We got maybe two or three a year - invariably they were fakes / people putting in their friends' details for a laugh / "opposed" people or local crazies wanting us to call on them etc. I remember one instance when I drove 40 miles to the end of our territory , eventually up a long farm track in a very rural area , to find it had been mailed in by a "born again Christian" type who rejoiced that his sole intention of mailing the slip was to waste 2 hours of my time and gas.
I shared this experience with the CO & he admitted that most congregation secretaries probably just binned the forms - the Society were never bothered and never followed up. And remember that these were people who had to buy a stamp and mail it in - not just spent a minute on a website filling in address details.