Unless Jagex are trying to screw with us, we're pretty confident now that the rumors are true: Mechscape will be called StellarDawn.
Here's some CSS code from the Jagex website:
background: silver url("https://www.jagex.com/img/crossservice/new_billing/paymentOptions/product_runescape.jpg");
background: silver url("https://www.jagex.com/img/crossservice/new_billing/paymentOptions/product_funorb.jpg");
background: silver url("https://www.jagex.com/img/crossservice/new_billing/paymentOptions/product_stellardawn.jpg");
(Thanks Lusidea from StellarDawn Community)