Removing Flash and adding Blink dagger I fear would might make it a must have item almost like Banshee Veil currently is and would reduce the amount the choices you have in selecting your items, this is especially true for TT maps where characters without a built in flash need to bring the summoner spell
Dash would be a short burst ghost then? Goes thru creeps, Immune to slows, run 100% faster for 3 seconds --- if its not at least about 100% run speed theres almost no reason to take it over ghost
Cleanse should probably last another second, at the very least add that extra second thru defensive mastery, just flat out buffing cleanse would just make it replace flash instantly
For Heal spell, Remove the aoe component from the original, add a defensive mastery point that increases the effectiveness of heal on yourself by 50%? and add a support mastery point that turns heal into aoe, healing for 50% of the amount healed on you... obviously make these 2 points fairly deep in both trees (meaning you cant take both)