I am strictly opposed to the 10% penalty on selling modules as an isolated change. This change needs to be accompanied by at least one of the following 3 options:
1) The ability to remove a module from a ship (without simultaneously selling that module), to carry that removed module around as cargo, to transfer that removed module to another ship, to transfer that module to or from personal storage in the station. Stations are already allowing us to store extra ships, this should be expanded to storing extra modules.
2) Some sort of simulator mode like Planetside 2's VR room where players can play around with any ship-and-fittings combination for free, but nothing that they do in this simulator mode counts for anything at all outside of simulator mode.
3) Some sort of in-game analogue to edshipyard.com. An in-game fitting tool of some sort. (EVE Online is implementing something like this that should be coming online in the next few months.)
If this change goes forward, the advice given to new players is going to look like this: "Modules can only be sold for 90% of their original purchase value, and you CAN NOT remove a module from your ship except to sell that module. Before buying any ship, go to edshipyard.com and plan out in advance what you want your final ship loadout to be, then buy the necessary modules only once. Do not purchase any expensive intermediary modules as a temporary solution as you're essentially paying 10% of the purchase cost of that intermediary module to have that module be a placeholder until you can get the final desired module."