Some interesting reading on the subject:
http://feedback.photoshop.com/photoshop_family/topics/multi_user_multi _computer
For single-user applications database does not appear to be a bottle-neck. From my own experience slow LR performance was quickly remedied by replacing my 5+ year old system with a new mid-range system platform. The bigger issue is why do some people with very high-end systems still have LR performance issues?
Does SQLite run the same in a multi-threaded environment, on every new processor platform, with every compatible OS? Given that Intel processor and I/O system technology changes about every six-months it's not surprising to me that a new system platform may have issues running processor or I/O intensive applications.
On my first job one of the designers developed a new floating point processor architecture that provided faster computations and better rounding accuracy. NSA was one of first customer to beta test a system with the new floating point processor. All of their applications ran a background system health monitor that used results calculated on a known good system. The monitor immediately detected the "more accurate" floating point data as a "system error." NSA refused to purchase the new system until we changed the floating point processor to match all of our other system's calculations.
Many years later Intel ran into a similar problem, which they claimed was not serious. It cost Intel about $450,000,000: