If you want to build a system that would use what Blockchain has to offer as a core feature or just a component, we'll be happy to do it with other Web/Mobile technologies we are working with, and connect the Web/Mobile App to smart contracts using the web3.js library. The workflow with smart contract dependant Web/Mobile Applications is a little different, as it is necessary to wait for the network consensus in order to move forward, so not all types of Applications work well with this technology.
Development of Web/Mobile Applications that use Blockchain
Swarm/IPFS
Using Blockchain is expensive. So it is important to put as little data on it as possible. Distributed file systems, come to the rescue, and we use them in our solutions. One is Swarm, the other is Interplanetary File System. What they allow is for files to be distributed between peers, on multiple boxes, much like a torrent file would be, so once it goes up, users don't need to worry about file becoming unavailable like it would be if a server went down. There is no such thing here.
Library driven development
In order to go arround the problem of not being able to debug and update code once it is published, we use the proposed solution of Library-driven development. In short, it is a concept that most code should reside in libraries, and referenced from the main contract. Those references can be changed, so in order to change the code in a library, we would just publish a new one and change the reference to point to it in the main contract.
Ethereum smart contracts development
Of all the available variant Blockchain technologies, for the time being, Ethereum is the most applicable. If you want to build a system that has no central point, and allows for different entities that do not trust each other to work together, Ethereum is solution for you.