I did try this approach with another member a few months back. They provided me an extract from LC and their gedcom, and I was able to match about 60%.
The harder part came when I had to put the matched data into a format that I could then load into the gedcom.
However, things have moved on now, if Alexander could produce (or modify an existing) report that had the census refs in the same format as LC, then matching would become a lot easier.
Yes I think this approach is better if we could match up a report from the website with a report from FTAnalyzer then the user could quickly see gaps.
The big problem is that the two sources contain different information. The Lost Cousins website has no information about the individual ids the family history program used it only had census references. Similarly FTAnalyzer only has the individual ids and some of the census references. Unfortunately very few people seem to add in census references in a sufficiently consistent format to ensure they are all picked up, so it would be extra work to suggest users retro fit their files with standardised census references.
So it's a bit of a catch 22 there is nothing specific on either the website or FTAnalyzer to definitely match up on and sadly that makes writing the reports in the exact same order a bit hit or miss. See the recent addition of the referrals report for an example of a close but not quite match.
Where we could speed things up would be for FTAnalyzer to generate a list of census entries you'd not entered onto Lost Cousins as it does at present, but in a format that could be loaded onto the website. If we were able to get that working then it could make it much easier for users to add new relatives if all they do is :
1) update the census in their tree
2) load GEDCOM into FTAnalyzer
3) export missing Lost Cousins file
4) load missing Lost Cousins file onto Lost Cousins website.
5) edit new entries on website to add extra info such as maiden name, have certificates etc.
The core issue here is creating a routine that presented the info in the correct format to the website and adding the extra code to the website to allow the import.
Note that data uploaded in this format may need an extra step for the user to confirm what was uploaded before committing the changes to the database. The data might also be worth flagging as FTAnalyzer generated so it was easy to track in the database. That might be useful as my experience is users are more likely to get things right if they have manually checked things than relying on an upload.
That said being able to mass upload missing entries could mean that the initial complaint that users often give for not entering data is that they have already entered it. That excuse would vanish as they would have a couple of clicks means of adding large numbers of new entries to the website. Which could mean hundreds of new additions a week and many more matches.