Clasificación condicional de Oracle SQL

Si entiendo correctamente, puede intentar usar CASE WHEN con sum función de ventana

CASE WHEN comprueba col3 no es null acumular otra cosa muestra NULL

CREATE TABLE T(
  col1 VARCHAR(5),
  col2 DATE,
  col3 DATE
);

INSERT INTO T VALUES ( 'a' , to_date('2018-01-20','YYYY-MM-DD') , to_date('2018-03-04','YYYY-MM-DD'));  
INSERT INTO T VALUES ( 'a' , to_date('2018-01-24','YYYY-MM-DD') , to_date('2018-04-04','YYYY-MM-DD'));  
INSERT INTO T VALUES ( 'b' , to_date('2018-01-02','YYYY-MM-DD') , to_date('2018-05-03','YYYY-MM-DD'));  
INSERT INTO T VALUES ( 'c' , to_date('2017-01-02','YYYY-MM-DD') , to_date('2017-05-08','YYYY-MM-DD'));  
INSERT INTO T VALUES ( 'd' , TO_DATE('2016-05-24','YYYY-MM-DD') , null);  
INSERT INTO T VALUES ( 'c' , TO_DATE('2018-02-05','YYYY-MM-DD') , to_date('2018-05-03','YYYY-MM-DD'));  
INSERT INTO T VALUES ( 'c' , TO_DATE('2018-07-28','YYYY-MM-DD') , null);  

Consulta 1 :

select t1.*,
    rank() OVER(partition by col1 order by col2 desc) rank1,
    (CASE WHEN COL3 IS NOT NULL THEN
       SUM(CASE WHEN COL3 IS NOT NULL THEN 1 ELSE 0 END) OVER(partition by col1 order by col2 desc)
    ELSE
       NULL
    END) rank2
FROM T t1

Resultados :

| COL1 |                 COL2 |                 COL3 | RANK1 |  RANK2 |
|------|----------------------|----------------------|-------|--------|
|    a | 2018-01-24T00:00:00Z | 2018-04-04T00:00:00Z |     1 |      1 |
|    a | 2018-01-20T00:00:00Z | 2018-03-04T00:00:00Z |     2 |      2 |
|    b | 2018-01-02T00:00:00Z | 2018-05-03T00:00:00Z |     1 |      1 |
|    c | 2018-07-28T00:00:00Z |               (null) |     1 | (null) |
|    c | 2018-02-05T00:00:00Z | 2018-05-03T00:00:00Z |     2 |      1 |
|    c | 2017-01-02T00:00:00Z | 2017-05-08T00:00:00Z |     3 |      2 |
|    d | 2016-05-24T00:00:00Z |               (null) |     1 | (null) |