Set up time: Almost no setup time or cost: at most installing a basic environment and or setting projects team.
Effective development phase: It is pretty much questionable if one can speak about effective or agile development phase for this scenario as setting up the business cases requires a lot of efforts as everything has to be implemented from scratch.
Architecture limit: Practical there is not architecture limit apart from some theoretical ones like uncountable languages. However on a long run there can be some practical limits, if the already implemented amount code needs to be reconstructed.
Figure 1. Technology curve for developing from basics.