If they were to opt for the C-Series over the current E-Jet as an example, the range of that aircraft opens up a world of new possibilities from LCY including US East Coast (tech stop required admittedly), Russia etc.. There is a niche for this airline, the C-Series could be the key to unlocking it.
Re the VLM sale, I'd imagine there is a non-compete clause on certain routes as a pre-condition of the sale to the VLM management. VLM will most likely retain a limited LCY presence whilst developing its network from Antwerp.