Hi @lorimer, the decentralization tool is a linear optimization tool and uses the available existing node machines, so it provides an good estimate whether the target topology can be achieved. It is true that there can be dead or degraded nodes, and nodes in maintenance, and that spare nodes are not yet included in the linear optimization, but we can make informed decision based on the tool. Application subnets (13 node subnets) require only gen1 nodes and as the tool shows (and also the IC dashboard) there is a huge pool of gen1 nodes with which application subnets can be formed, while still keeping enough spare nodes. It also shows (as we discussed in this previous forum post) that the number of (spare) Gen2 node machines is rather limited, making it not possible to add any larger subnets at the moment (with 28 nodes machines or more).
Actually achieving target topology requires numerous node replacement proposals (subnet management proposals) which it was agreed in the same thread would be achieved by the weekly subnet management proposals that replace dead nodes. This of course will happen over time and the speed of which will depend on how many subnet replacement proposals are needed every week.