I don't have any up to date experience of Echo or Husqvarna, as I ceased being a main dealer for those brands more than 15 years ago and registering machines wasn't even thought of back then.
The only other manufacturer that I am a dealer for, that insists a product sale is registered with them via a secure dealer portal is Hayter/Toro- again for the same reasons Stihl stipulate. Both systems work well, particularly if we have a machine brought in under warranty that we haven't originally sold and the owner has mislaid paperwork. With a recognised form of ID we can confirm ownership and crack on knowing we will be paid for our work.
Sure, a manufacturer will get a lot of valuable marketing info via us registering machines, but unless we tick a box when registering a machine stating the customer is happy to receive marketing material, then it just doesn't happen and they are not bothered by the manfacturer or their associates
Both systems work very well. We have had a few 'dubious' call from people with a nearly new Stihl or Hayter/Toro that they state are under warranty, but they can't find their receipt but can we look at it anyway? We point out to them a receipt isn't necessary, but proof of ID is that matches their details on the database before we can look at it, and we more often that not never see them bring it in. Is that because it's stolen- I don't know, but it could be a deterrent to bringing them in, rather than a deterrent having them stolen in the first place.
Authorities do/should know about these invaluable databases held by manufacturers, and the help they provide tracking owners.
Your database is a good idea, but I can see members being concerned as to the security of their details and the possible misuse of their data. Admittedly that could be no different from what could happen from a manufacturer, but at least there's a good reason to register a product (the warranty) and manufacturers are held to a legal account regarding data. If a machine is out of warranty and insured, then stolen, it probably has paid for itself and been written down to nothing on the books anyway (I am not referring to large plant here- more your mowers and hand held stuff- the most popular stuff that is lifted) so after three years or more, if it's nicked it's not quite a big deal aside from inconvenience. lets' be honest we rarely get emotionally attached to a chainsaw (well some might) which could be another mitigating factor to register it with you.