may need some stability improvements but this seems like a step in the right direction

gistfile1.txt

ObjectFactory.Initialize(fun x -> x.AddRegistry (new SearchRegistry()))

let write<'T> item =
    ObjectFactory.GetAllInstances<Indexer<'T>>()
        |> Seq.iter (fun idxr -> idxr.Index item)

let itemsToIndex<'T when 'T:null and 'T:not struct and 'T:equality> =
    let p = QueueProvider<'T>.Create()
    seq {
        while true do
            let obj = p.Dequeue()
            if not (obj = null) then yield obj
            else Thread.Sleep 1500
    }

try
    seq {
        yield async { itemsToIndex<Recipe> |> Seq.iter write }
        yield async { itemsToIndex<Malt> |> Seq.iter write }
        yield async { itemsToIndex<Hop> |> Seq.iter write }
        yield async { itemsToIndex<Addition> |> Seq.iter write }
        yield async { itemsToIndex<Yeast> |> Seq.iter write }
    }
    |> Async.Parallel
    |> Async.RunSynchronously
    |> ignore

finally
    SearchRegistry.DeRegister()