When I arrived we had LW and HS98. I found the supplements difficult to use logistically, as many people had a hard time juggling a bulletin, a hymnal, and a supplement. My first attempt to solve this was to try doing a service completely out of the supplement every once in a while, but this was difficult to pull off due to the limited hymn selection. We ended up just printing up anything from the supplement that we wanted to use, but this was still unwieldy.
We currently have LSB, and it has been very well received. We typically use the hymnal itself for all the liturgy and hymns. We have Lutheran Service Builder, but we only print the entire service for holidays.
If a supplement were to be produced in any form, I don't think we need another setting of the Divine Service. Frankly, I think five is a bit much. I can understand how we got to this point, but I think the fewer the better. The one place where I could see a helpful supplement to the liturgy is the "Service of Prayer and Preaching." I've found this quite awkward to use, particularly with the canticles. It would be helpful to have another option for a catechetical service.
As far as the hymns, I'm always happy to consider adding new hymns to the repertoire. The simplest thing would be an electronic supplement, but I realize that those that are not printed in the hymnal are not likely to be used. I do use the electronic/accompaniment volume only hymns in LSB from time to time, but this is usually with a hymn that I already know.
As a pastor, what would be most useful to me is the anticipated companion volume, "LSB Desk Edition:Liturgy" referenced in the Altar Book, but still unavailable.