I am currently running a SR4A game and we are at least a year out RL from 2075, however I thought it might be better to gradually shift my game from 4 to 5. In most areas, the shift will be rather seamless. Not so much with the Matrix. I could use some transition/retcon advice on moving my game from 4 to 5e.
I thought SR4 did a really good job in reflecting the current changes in technological development (AR is already becoming a reality via smartphones and google glass). More than just changing the very nature of the Matrix to something that made a lot more sense in light of modern technology, the Crash 2.0 was a very clear event that would indeed call for a very rapid and dramatic change to the existing Matrix infrastructure.
There really isn’t a clear demarcation between Matrix 2.0 and 3.0 (as it is nearly as big a change to the underlying infrastructure of the the Matrix as from 1.0 to 2.0). More importantly, a change that large would require an investment of nuyen to nearly rival that of the post crash recovery. Additionally, switching from a wireless mesh network that did not require much in the way of physical telephony to a grid based architecture (I am inferring from the fluff it would be more of a cellular type design) would require massive roll out in both time and manpower. Finally, making a drastic overnight switch is just asinine from a business perspective. If you are able to put out your first gen Matrix 3 system today, you wouldn't begin to think of phasing out your Matrix 2 equipment until the end of its life-cycle (a minimum of two years if you use the current cellphone contracting system as a model). The return of the cyberdeck might be great from a grognard meta-game perspective, but an utterly ridiculous stumble backwards as a technology design model and just doesn't make sense from a story perspective.
One thing I have already begun to implement is that cyberdecks never went away. The current commlinks listed in the books are in fact not commlinks but cyberdecks and as a cyberdeck they function exactly as described. Commlinks have much lower processing power. A commlink with a system of 5 cannot run 5 programs before its response degrades but 5 points of programs before its response degrades. So it is good running a stealth 3 program, but add on a encrypt 3 (for a total of 6 rating points) and its response drops.