I'm not talking about transferring woes but rather the technicality of these 2 wallets existing on the very same PC.
This was also one of the reason why most users who was using Electrum for their BTC didn't use Electron Cash for their BCH (Most chose some other wallet for their BCH at the start).
Is there still any sort of issue after Electron Cash actually actively update their code to the current latest version?
I believe the concern was initially about the fear of having to compromise your Electrum simply installing another software on your system. To be on a safe side, that is why a lot of those precautions had to be sounded with loud voice and also don't forget that initially it was called Electrum cash before it was changed to Electron cash for the sake of clarity.
Even at that time, every one was advised to send his bitcoin to another wallet first before trying to claim so the initial wallet is empty. I can say its originally due to the uncertainty that prevail around the time since its the first time a major fork will be happening. Since then, I haven't heard the clash of the two especially if you download from the official sites of both.