It is still possible to short the stock in T4T.
However, illegal shorting - that is naked shorting, or shorting with shares that do not exist / are not in the coffers of the market makers - is much ore difficult or impossible with this system.
A most basic level explanation of this: (I assume you already know this, but I did not when I started here so I hope this helps someone)
understand first that here are shares in the hands of shareholders like you and I, and there are shares in the hands of market makers.
Now if I wanted to short sell a stock I use the shares in the reserves of the market makers - I first issue a short sell on these shares, then I "cover" - usually within 3 days by buying the shares back. As can be seen, if the price of the shares I originally "sold" drops before I cover with my buy, there is money left on the table for me to put in my pocket (because I can buy back the original number of shares for a cheaper price and immediately return these shares to the market maker). Really, the shares are kind of borrowed for a few days (sold, but only for a short period of time).
Now - If I really wanted to profit, it might be wise to send some drones out on message boards and convince everyone out there that the stock is a total POS, threaten lawsuits so that people are afraid to buy, say the CEO is swindling investors and so forth.
So , I guess the main thing T4T does is to ensure MMs actually have shares for the short sellers to borrow in the first place. Keeps things a little more legal.
This is a VERY basic explanation - admittedly. Hope this helps someone out there as Tytan is T4T and this might help understand one difference with T4T trading.
All IMO - of course
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