This is a good idea, however, CutScene editor isn't available as far as i know (so you can't control cameras etc.)... Maybe including Bink format back is a good idea, but it will also require engine to know filename of bink library, load it into memory, etc. In other words... Maybe it will be simplier if you'll use TR level manager for videos? 
And about "bonus secret level" feature. Please check out this test executable: _initiator.nm.ru/tr/patche...tlevel.rar . It modifies END_LEVEL trigger behaviour - if you have less than 3 secrets, user-defined level number will be used, and if you have 3 secrets - level number 6 will load. So, for example, you can place a trigger with END_LEVEL set to 39 and if player have less than 3 secrets, he will jump to credits, and if he have 3 secrets, he will jump to level number 6. Note that secrets amount will reset in this case, or else player will stuck forever in secret level (because every time he will step onto any END_LEVEL trigger in secret level, he will jump to the beginning of this secret level again).
This executable seems to be compatible with TREP. But anyway, if it will work fine, then this feature will be included in TREP.
EDIT:
Sorry again, just bombing you with another request to test increased flyby sequences limit
.
Please download this test executable and test flyby sequences above 8. Now it should work with more than 8 sequences and new theoretical limit is 64. But i still haven't tested maximum num. of cameras (it looks like TR4 uses fixed memory region to load flyby cameras, i. e. it must be remapped too), so maybe there will be bugs and crashes if you will use too much cameras.
And about "bonus secret level" feature. Please check out this test executable: _initiator.nm.ru/tr/patche...tlevel.rar . It modifies END_LEVEL trigger behaviour - if you have less than 3 secrets, user-defined level number will be used, and if you have 3 secrets - level number 6 will load. So, for example, you can place a trigger with END_LEVEL set to 39 and if player have less than 3 secrets, he will jump to credits, and if he have 3 secrets, he will jump to level number 6. Note that secrets amount will reset in this case, or else player will stuck forever in secret level (because every time he will step onto any END_LEVEL trigger in secret level, he will jump to the beginning of this secret level again).
This executable seems to be compatible with TREP. But anyway, if it will work fine, then this feature will be included in TREP.
EDIT:
Sorry again, just bombing you with another request to test increased flyby sequences limit
.Please download this test executable and test flyby sequences above 8. Now it should work with more than 8 sequences and new theoretical limit is 64. But i still haven't tested maximum num. of cameras (it looks like TR4 uses fixed memory region to load flyby cameras, i. e. it must be remapped too), so maybe there will be bugs and crashes if you will use too much cameras.
