Hi Adam. I have been messing about with some of the equations from that paper I mentioned above for the last few days. I thought, perhaps, that if the mass loss from the universe could be written into omega (matter) in equation (1) as something like omega (matter) = -kt + c for some time interval between, say, t1 and t2 (constant k>0 and c to be determined), then we could substitute this into equation (1) with omega (lamda) = 0 (i.e. no dark energy component but instead the matter density is decreasing constantly with time, that is the universe is losing mass). I found, though, that this doesn’t work and so it kind of blows my idea out of the water! The issue is that the second time derivative of the expansion factor d^2 a(t) / dt^2 < 0 which means that even though the universe continues to expand it does so at an ever decreasing rate. Of course, for the model with lamda the change in the rate of expansion goes from decreasing to zero to increasing.
I hope this makes sense.