And I tell you, you are Peter, and on this rock I will build my church, and the gates of hell shall not prevail against it. I will give you the keys of the kingdom of heaven, and whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven.” (Mt. 16:18-19)
Ecclesiology technically speaking is just a doctrine of the church. One can have low church ecclesiology, or high church ecclesiology. As long as one has thought upon the matter and formulate a doctrine of how the church relates to God and to the individual Christian, then one has an ecclesiology, technically speaking.
However, there is another way to understand ecclesiology, the biblical, more restrictive way. In the Scriptures, the Church is treated as an organism AND institution. Only in an institution can one has offices like elders and deacons, whose jurisdiction cannot be indefinite and unlimited as they need to know who they are serving. And in order for proper pastoral care and church discipline to work, or even just deciding on matter related to the local church, there must be membership in order for that to happen. Thus, the [Visible] Church in the biblical sense must be institutional in some sense. We further note that biblical authority flows from Christ to the church and then to the individual, and that is not Roman Catholicism! God gave officers as gifts to the church (Eph. 4:11), which imply that the authority does not come "from the bottom up, from members to the officers," but that officers of the Church derive their authority from God and not by popular consent. The Church is NOT a democracy! The members of the church are involved only for validation, not that they actually vote a person into office like how a citizen vote for the country's prime minister.
If that is the biblical ecclesiology, then any sect that does not pay attention to the institutional aspects of the Church are deficient in ecclesiology. It does not matter how much they talk about "the church," because they aren't really talking about the Church, the Church as God knows, loves and cares for through her ordained offices.
Thus, while the Brethren movement especially John Darby focuses on "the church," it can be said that his ecclesiology is little to non-existent, since he does not deal with the Church which God loves. While "schismatic" might be a strong word, the reality is not too far for those who spurn God's offices and His Church for a mere shadow of a Christian assembly. Let me put it bluntly: a group of Christians coming together is NOT necessarily a church. A group of Christians coming together for fellowship at Starbucks, complete with sharing devotions, is not a church. A group of Christians coming together at a member's home for worship and bible study, is not a Church. A group of Christians coming together to have a memorial "Lord's Supper" is not a Church. A Church is where God rules and reigns through the ordained ministers, elders and deacons He gave to His Church! No ordination, no Church! God may be present of course, since God is always present where two or three Christians come together for prayer (Mt. 18:20), but that is not the Church. God after all is omnipresent, so just because God works salvation through sharing of testimony does not make the gathering where the testimony is shared is the Church.
Thus, as far as I am concerned, and as I understand Scripture to teach, many of the low church brethren and the modern house church movements have little to no true biblical ecclesiology. On the extreme end of overt anti-institutionalism, the modern day house church movement in the West that used to be shepherded by people like Frank Viola (which are not the same as churches that meet in homes because of necessity in places like China) are no churches at all. They have no real offices and no ordained ministers, thus they are not real churches. Since they are not churches, their baptisms are invalid and their "Lord's Supper" sacrilegious, a mockery of the true sacrament instituted by Christ. To partake in such "Lord's Suppers" therefore is sin.
Of course, this side of heaven, not all churches can match the ideal, although we are called to that ideal. Imperfections mar Christ's bride this side of glory. Yet, it is one thing to have an imperfect system with imperfect ordination standards and views, and another to reject ordination altogether. It is one thing to be low church, and another to be "no-church" and be fully anti-institutional. The former can be seen as struggles of the church militant, but the latter is betrayal of the church militant. Failure to see this leads one either to perfectionism with regards to ecclesiology, or to rejection of biblical ecclesiology altogether since it's unattainable.
Thus, when I mention that somebody or some movement has "little to no ecclesiology," I mean they have no true biblical eccleiology, in the second sense of the term. Some of course might have no ecclesiology in the first sense of the term, but for me there aren't really much difference between both senses of the term since the [Visible] Church that God loves is not being discussed anyway.
UPDATE: I was informed that Frank Viola is no more shepherding the Organic Church movement, although it does not seem he has changed his views on the topic, as he has stated here. Instead, the current leader if you will of the Organic Church movement is Neil Cole. With this information, I have modified the post accordingly