In the org.apache.sis.feature package, a DefaultFeature can contains an attribute which itself contains a characteristic having the AttributeConvention.CRS_CHARACTERISTIC name. The value of that characteristic is the Coordinate Reference System (CRS) of the geometry that this attribute can contains. However there is currently no verification that a geometry given to that attribute has the expected CRS. We should add a verification mechanism, compatible with both JTS and ESRI API. This may require Java reflection code, since those two libraries are optional.
One open question is where to store the CRS information in the geometry object. JTS has a SRID property, but it is only an int type. It could be decided that the integer value is the EPSG code, but this is an arbitrary (while common) decision. Alternatively we could use the JTS user object for storing the full CoordinateReferenceSystem object, but this is another arbitrary decision.