Sounds a reasonable thing to do, Don.
As a non-member, I don't have any insight into when the "LDS" mail would be used and when the public / FS mail would be used. Is it possible to outline how the system (if it is the system) would decide which to use or am I missing the point of how it would be used?
Are you referring to being able to having (ie. allowing the use of) MULTIPLE "E-mail" Addresses associated with 'FamilySearch'?
IF, so; THEN, with ALL the associated "Parts" of 'FamilySearch', I would suggest that that may be a 'tall order' ...
Most Users/Patrons have ONLY one "E-mail" Address; and, some struggle with just that.
Personally, I do not feel that 'FamilySearch' needs to go to that extent; as, there is ALREADY "User Messaging" in 'FamilySearch'; and, provided a User/Patron enables such, the User/Patrons WILL receive "E-mails" when 'Message(s)' are sent through "User Messaging" in 'FamilySearch' and have has been received.
And, the aforementioned works quite well in the "Mobile" Application version of 'FamilySearch'.
In fact, I get the "Notifications" of such 'Messages', through "User Messaging" in 'FamilySearch', through the "Mobile" Application version of 'FamilySearch', on my "Mobile" Phone; BEFORE, I get an "E-mail" NOTIFICATION.
Personally, I think having MULTIPLE "E-mail" Addresses associated with one's 'FamilySearch' Account would ONLY complicate matters; especially, for 'FamilySearch'.
Just my thoughts.
ps: I have, both, a PRIMARY "E-mail" Address; and, an associated ALIAS "E-mail" Address (which I use in 'FamilySearch'), this causes some problems/issues with regard to 'FamilySearch'; so, I think that the use of MULTIPLE "E-mail" Addresses in 'FamilySearch' would be, as bad; or, worse.
I totally understand ...
We all get those, Junk; and, Scam, e-mails ...
It is just, with my experience with more than one associated "Email" Address in 'FamilySearch', there ARE problems/issues.
Just a 'heads-up' ...
ps: Technically, 'FamilySearch; ONLY allows ONE "E-mail" Address to be associated with your 'FamilySearch' Account (eg. just like your 'Church' Account).