The lack of any improvement to the reverb and delay is probably the main drawback.
The Behringer X32 rack is the obvious alternative - much better effects but I don't like its app (though admittedly I haven't spent much time with it). The Mackie app seems far superior and that is critical when you don't have physical faders.
Anybody had good or bad experiences in stepping up from the 1608.
Fluddman, full disclosure that this reply is an unabashed prop for the X32 Rack in particular.
An X32 Rack is technically a larger mixer than a DL1608 with the additional 6 aux inputs & outputs as standard across all the X32 line, though not full mic pres these can still be useful for incorporating line ins, DI, or analog sub mixers, and furthermore rerouted to channels 17-32 for the additional processing benefits of those channels. Of course there is the additional cost from rental or purchase from the choice of a suitable expansion unit if 17plus mic pres are required, at a future time when necessary.
I offer from experience, testament and personal conviction to the absolute superior speed that the UI of the X32Mix and MixingStation apps provide, in particular navigating beyond 16 channels to a full 32 mics, 6 aux, and minimum 4 stereo effects. While I have waxed poetic to the design of MF Classic in this and other forums, the MF UI suffers in navigation speed along with other similarly designed manufacturers remote UI apps with the constant lateral channel navigation swiping of a full 32 plus channels. It is the combination of the superior navigation speed, access to facilities, and proven stability & reliability that IMO, the Music Group X/M Mix and the 3rd party MixingStation Donate apps prove superior to any and all remote product design specific apps for digital audio performance mixers, though not meant or to be taken as a slight against the Mackie MF Classic / DL32 apps, still a work of art in product design, of course IMHO.
In regards to the effects comparison, there is no amount of window dressing or doctoring to the DL effects, reverb in particular, that can compete with the
X/M32 series. Thought to ponder; I propose that once upon a time that the design, manufacture and sale of a rack box with the X/M32 resident insert effects/
processors at the current USD street price of an X32 Rack would have been possible. Point being that the quality and choice of the X/M32 FXs are so far superior to the DL line and are worthy of consideration alone.
I would suggest that whatever upgrade path you may pursue, that the DL1608 would/could be your backup option, situation allowing of course.
Cheers